ATW Atwood Oceanics, Inc. (delisted)

SUMMARY

         This summary highlights information contained elsewhere in this joint proxy statement/prospectus. Ensco and Atwood urge you to read carefully the remainder of this joint proxy statement/prospectus, including the attached annexes and the other documents to which we refer to herein and documents incorporated by reference into this joint proxy statement/prospectus, as this section does not provide all the information that might be important to you with respect to the merger and the other matters being considered at the Ensco general meeting or Atwood special meeting, as applicable. See also the section entitled "Where You Can Find More Information" beginning on page 178. We have included page references to direct you to a more complete description of the topics presented in this summary.

The Companies (See page 141)

Ensco plc

        Ensco is a global offshore contract drilling company and one of the leading providers of offshore contract drilling services to the international oil and gas industry. Ensco owns and operates an offshore drilling rig fleet of 53 rigs, with drilling operations in most of the strategic markets around the globe. Ensco also has two rigs under construction. For the three and six months ended June 30, 2017, Ensco's operating revenue totaled approximately $457.5 million and $928.6 million, respectively. For the year ended December 31, 2016, Ensco had annual revenue of approximately $2.8 billion and employed approximately 4,900 personnel.

        The Ensco Class A ordinary shares are listed on the NYSE under the symbol "ESV." Ensco is a public limited company organized under the laws of England and Wales. Ensco's principal executive offices are located at 6 Chesterfield Gardens, London, W1J 5BQ, United Kingdom and its telephone number is 44 (0) 20 7659 4660.

        Additional information about Ensco and its subsidiaries is included in documents incorporated by reference in this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 178.

Echo Merger Sub LLC

        Merger Sub, a wholly owned subsidiary of Ensco, is a Texas limited liability company formed on May 26, 2017 for the purpose of effecting the merger. Under the merger agreement, Merger Sub will merge with and into Atwood, with Atwood continuing as the surviving company and a wholly owned subsidiary of Ensco. Merger Sub has not conducted any activities other than those incidental to its formation and the matters contemplated by the merger agreement, including the preparation of applicable regulatory filings in connection with the merger.

Atwood Oceanics, Inc.

        Atwood is a global offshore drilling contractor engaged in the drilling and completion of exploratory and developmental oil and gas wells. Atwood currently owns a diversified fleet of 10 mobile offshore drilling units located in the Mediterranean Sea, offshore West Africa, offshore Southeast Asia and offshore Australia. Atwood recently executed a sale and recycling agreement with respect to one of the drilling units. For the three and nine months ended June 30, 2017, Atwood's operating revenue totaled $117 million and $442 million, respectively. For the year ended September 30, 2016, Atwood's operating revenues totaled $1.0 billion and Atwood employed 938 personnel.

        The Atwood common stock is listed on the NYSE under the symbol "ATW." Atwood's registered office and principal executive offices are located at 15011 Katy Freeway, Suite 800, Houston, Texas 77094 and its telephone number is (281) 749-7800.

        Additional information about Atwood and its subsidiaries is included in documents incorporated by reference in this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 178.

The Merger (See page 49)

        The merger agreement provides that Merger Sub will merge with and into Atwood, with Atwood continuing as the surviving company and a wholly owned subsidiary of Ensco. The terms and conditions of the merger are contained in the merger agreement, which is attached as Annex A to this joint proxy statement/prospectus. Please carefully read the merger agreement as it is the legal document that governs the merger.

Merger Consideration (See page 99)

        Subject to the terms and conditions set forth in the merger agreement, at the effective time of the merger (the "Effective Time"), each share of Atwood common stock issued and outstanding immediately prior to the Effective Time will be converted into the right to receive 1.60 Ensco Class A ordinary shares. The merger agreement does not contain any provision that would adjust the exchange ratio based on the fluctuations in the market value of either the Atwood common stock or Ensco Class A ordinary shares. Because of this, the implied value of the merger consideration to the Atwood shareholders will fluctuate between now and the completion of the merger.

        The market price of the Ensco Class A ordinary shares and the Atwood common stock will fluctuate prior to the completion of the merger. You should obtain current stock price quotations for Ensco Class A ordinary shares and Atwood common stock.

Treatment of Atwood Equity-Based Awards (See page 100)

        Pursuant to the terms of the merger agreement, each award of Atwood restricted stock units other than any Atwood restricted stock units that are required to be settled in cash ("Atwood RSUs") that is outstanding as of immediately prior to the Effective Time shall vest upon the Effective Time. As soon as practicable after the Effective Time, the Atwood RSUs will be settled through the issuance to the holders thereof of Ensco Class A ordinary shares in an amount equal to the number of shares of Atwood common stock originally subject to such award multiplied by the exchange ratio (rounded down to the nearest whole share). Each award of Atwood restricted stock units that is required to be settled in cash ("Atwood Cash Units") will be treated in accordance with the terms of such award.

        Each award of Atwood stock options that remains outstanding and unexercised immediately prior to the Effective Time (an "Existing Option"), will, as of the Effective Time, automatically and without

any further action being required, be converted into a stock option relating to the Ensco Class A ordinary shares, on the same terms and conditions (including the same expiration restrictions) as were applicable to such Existing Option immediately prior to the Effective Time (a "Converted Option"), except that (i) the number of Ensco Class A ordinary shares subject to the Converted Option will be determined by multiplying the number of shares of Atwood common stock subject to the corresponding Existing Option immediately prior to the Effective Time by the exchange ratio, and then rounded down to the nearest whole share, and (ii) the exercise price per share of the Converted Option will equal the per share exercise or strike price of the Existing Option immediately prior to the Effective Time divided by the exchange ratio, rounded up to the nearest whole cent.

Material U.S. Federal Income Tax Consequences (See page 130)

        In general, subject to the discussion relating to the potential application of Section 304 of the Internal Revenue Code under the section entitled "Material United States Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to Atwood Shareholders," the receipt by U.S. holders (as defined in the section of this joint proxy statement/prospectus entitled "Material United States Federal Income Tax Consequences of the Merger") of Ensco Class A ordinary shares pursuant to the merger should be a taxable exchange for U.S. federal income tax purposes. Assuming such treatment, a U.S. holder generally will recognize capital gain or loss equal to the difference between (i) the fair market value of the Ensco Class A ordinary shares received as consideration in the merger on the date of the exchange and (ii) the holder's adjusted tax basis in the shares of Atwood common stock surrendered in the exchange. A U.S. holder's adjusted basis in its shares of Atwood common stock generally will equal such holder's purchase price for such shares, as adjusted to take into account stock dividends, certain non-dividend distributions, stock splits and similar transactions. For further information, please refer to "Material United States Federal Income Tax Consequences of the Merger."

        A non-U.S. holder (as defined in the section of this joint proxy statement/prospectus entitled "Material United States Federal Income Tax Consequences of the Merger") generally should not be subject to U.S. federal income tax on any gain recognized in the merger other than in certain specific circumstances (including as a result of the potential application of Section 304 of the Internal Revenue Code), as further described under the section of this joint proxy statement/prospectus entitled "Material United States Federal Income Tax Consequences of the Merger—Tax Consequences of the Merger to Atwood Shareholders."

         The United States federal income tax consequences described above may not apply to all Atwood shareholders. Your tax consequences will depend on your individual situation. Accordingly, we strongly urge you to consult your tax advisor for a full understanding of the particular tax consequences of the merger to you.

Ensco General Meeting (See page 33)

        The Ensco general meeting will be held at the offices of Slaughter and May, One Bunhill Row, London EC1Y 8YY, England, at 3:00 P.M. (London time) on October 5, 2017.

        All Ensco shareholders of record at the close of business in London on August 23, 2017, the Ensco record date, are entitled to notice of, and to attend and vote at, the Ensco general meeting or, subject to the Ensco Articles of Association, any adjournments or postponements of the Ensco general meeting. This joint proxy statement/prospectus is being sent to Ensco shareholders beginning August 21, 2017.

        At the Ensco general meeting, Ensco shareholders will be asked to approve, in addition to all subsisting authorities:

1.

the Ensco Merger Consideration Proposal (see page 38);



2.

the Ensco General Allotment Authority Increase Proposal (see page 39);



3.

the Ensco General Disapplication of Pre-emptive Rights Proposal (see page 42); and



4.

the Ensco Specified Disapplication of Pre-Emptive Rights Proposal (see page 42).

        As a U.K. company publicly traded on the NYSE, Ensco shareholder approval of the Ensco Merger Consideration Proposal is subject to the shareholder approval requirements under both the Companies Act 2006 and NYSE rules. The Ensco Merger Consideration Proposal is being proposed as an ordinary resolution. Assuming a quorum is present, such proposal will be approved for purposes of the Companies Act 2006 and NYSE rules if a majority of the votes cast are cast in favor thereof. The Ensco General Allotment Authority Increase Proposal will be proposed as an ordinary resolution and, assuming a quorum is present, will be approved if a majority of the votes cast are cast in favor thereof. Each of the Ensco General Disapplication of Pre-emptive Rights Proposal and the Ensco Specified Disapplication of Pre-emptive Rights Proposal will be proposed as a special resolution, which means, assuming a quorum is present, each such proposal will be approved if at least 75% of the votes cast are cast in favor thereof.

        Approval of the Ensco Merger Consideration Proposal is required for completion of the merger. Approval of the other Ensco proposals set forth above is not required in order to complete the merger.

        In connection with the Ensco general meeting, abstentions and broker non-votes will be considered in determining the presence of a quorum. While abstentions and broker non-votes are not considered votes cast under the Companies Act 2006, under NYSE rules abstentions, but not broker non-votes, will be considered as votes cast for determining whether a sufficient number of votes have been cast on a particular proposal. As a result, for purposes of determining whether the Ensco Merger Consideration Proposal has been approved in accordance with the Companies Act 2006, abstentions and broker non-votes will not have any effect on the outcome of the vote. With respect to NYSE rules, abstentions will have the same effect as votes cast "AGAINST" the Ensco Merger Consideration Proposal and broker non-votes will not have any effect on the outcome of the vote. Abstentions and broker non-votes will have no effect on the outcome of the Ensco General Allotment Authority Increase Proposal, the Ensco General Disapplication of Pre-emptive Rights Proposal or the Ensco Specified Disapplication of Pre-emptive Rights Proposal.

        As of August 17, 2017, directors and executive officers of Ensco and its affiliates had the right to vote approximately 1,903,037 Ensco Class A ordinary shares, or approximately 0.63% of the outstanding Ensco Class A ordinary shares on that date.

        After careful consideration, on May 29, 2017, the Ensco Board unanimously determined that the form, terms and provisions of the merger agreement and the transactions contemplated thereby, including the merger and the allotment and issuance of the Ensco Class A ordinary shares, are advisable, fair and reasonable to and in the best interests of Ensco and its shareholders. The Ensco Board unanimously recommends that Ensco shareholders vote "FOR" the Ensco Merger Consideration Proposal. For a more complete description of the recommendation of the Ensco Board with respect to the Ensco Merger Consideration Proposal, see "The Merger—Ensco's Reasons for the Merger; Recommendation of the Ensco Board of Directors" beginning on page 57.

         In addition, the Ensco Board recommends that Ensco shareholders vote "FOR" the Ensco General Allotment Authority Increase Proposal, "FOR" the Ensco General Disapplication of Pre-Emptive Rights Proposal and "FOR" the Ensco Specified Disapplication of Pre-Emptive Rights Proposal.

Atwood Special Meeting (See page 45)

        The Atwood special meeting will be held at 15011 Katy Freeway, First Floor, Houston, Texas 77094, at 9:00 A.M. (Houston time) on October 5, 2017. Only Atwood shareholders of record at the close of business on August 23, 2017, the Atwood record date, are entitled to notice of, and to vote at, the Atwood special meeting and any adjournments or postponements of the Atwood special meeting.

        At the Atwood special meeting, Atwood shareholders will be asked to consider and approve:

1.

the Atwood Merger Proposal (see page 49);



2.

the Atwood Compensatory Proposal (see page 139); and



3.

the Atwood Adjournment Proposal (see page 140).

        The Atwood Merger Proposal requires the approval of Atwood shareholders holding at least two-thirds of the Atwood common stock entitled to vote thereon pursuant to the requirements of the TBOC. Assuming a quorum is present, the Atwood Compensatory Proposal requires the approval of a majority of votes cast by the Atwood shareholders present, in person or by proxy, at the Atwood special meeting. Whether or not a quorum is present, the Atwood Adjournment Proposal requires the approval of a majority of votes cast by the Atwood shareholders present, in person or by proxy, at the Atwood special meeting.

        Approval of the Atwood Merger Proposal is required for completion of the merger. Approval of the other Atwood proposals set forth above is not required in order to complete the merger.

        In connection with the Atwood special meeting, abstentions and broker non-votes will be considered in determining the presence of a quorum. Abstentions and broker non-votes will have the same effect as votes cast "AGAINST" the Atwood Merger Proposal, but will have no effect on the outcome of the Atwood Compensatory Proposal or the Atwood Adjournment Proposal.

        As of August 17, 2017, directors and executive officers of Atwood and its affiliates, had the right to vote approximately 491,689 shares of Atwood common stock, or approximately 0.61% of the outstanding shares of Atwood common stock on that date.

        After careful consideration, on May 29, 2017, the Atwood Board unanimously determined that the merger agreement and the transactions contemplated by the merger agreement, including the merger, are advisable and in the best interests of Atwood and its shareholders. The Atwood Board unanimously recommends that Atwood shareholders vote "FOR" the Atwood Merger Proposal . For a more complete description of the recommendation of the Atwood Board with respect to the Atwood Merger Proposal, see "The Merger—Atwood's Reasons for the Merger; Recommendation of the Atwood Board of Directors" beginning on page 59.

         In addition, the Atwood Board recommends the Atwood shareholders vote "FOR" the Atwood Compensatory Proposal and "FOR" the Atwood Adjournment Proposal.

Opinion of Financial Advisor to Ensco (See page 63 and Annex B)

        On May 29, 2017, at a meeting of the Ensco Board, Morgan Stanley & Co. LLC ("Morgan Stanley") rendered its oral opinion to the Ensco Board, subsequently confirmed by delivery of a written opinion, dated May 29, 2017, that, as of that date, and based upon and subject to the various assumptions made, procedures followed, matters considered and qualifications and limitations on the scope of review undertaken as set forth in the written opinion, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to Ensco.

        The full text of the written opinion of Morgan Stanley to the Ensco Board, dated as of May 29, 2017, is attached as Annex B to this joint proxy statement/prospectus and is incorporated herein by

reference in its entirety. The summary of the opinion of Morgan Stanley in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the opinion. You should read Morgan Stanley's opinion, this section and the summary of Morgan Stanley's opinion carefully and in their entirety for a discussion of the assumptions made, procedures followed, matters considered and qualifications and limitations upon the review undertaken by Morgan Stanley in rendering its opinion. Morgan Stanley's opinion was directed to the Ensco Board, in its capacity as such, and addressed only the fairness from a financial point of view to Ensco of the exchange ratio pursuant to the merger agreement as of the date of such opinion.

        Morgan Stanley's opinion did not address any other aspects or implications of the merger. Morgan Stanley's opinion did not in any manner address the price at which the Ensco Class A ordinary shares would trade following the merger or at any time, and Morgan Stanley expressed no opinion or recommendation to any holder of Ensco Class A ordinary shares or Atwood common stock as to how such holder should vote at the Ensco general meeting or the Atwood special meeting, respectively, or whether to take any other action with respect to the merger.

Opinion of Financial Advisor to Atwood (See page 75 and Annex C)

        Goldman Sachs & Co. LLC ("Goldman Sachs") delivered its opinion to the Atwood Board that, as of May 29, 2017 and based upon and subject to the factors and assumptions set forth therein, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to the holders (other than Ensco and its affiliates) of shares of Atwood common stock.

        The full text of the written opinion of Goldman Sachs, dated May 29, 2017, which sets forth assumptions made, procedures followed, matters considered and limitations on the review undertaken in connection with the opinion, is attached as Annex C to this joint proxy statement/prospectus. Goldman Sachs provided its opinion for the information and assistance of the Atwood Board in connection with its consideration of the transaction. The Goldman Sachs opinion is not a recommendation as to how any holder of shares of Atwood common stock should vote with respect to the transaction or any other matter. Pursuant to an engagement letter between Atwood and Goldman Sachs, Atwood has agreed to pay Goldman Sachs a transaction fee that is estimated, based on the information available as of the date of announcement of the transaction, at approximately $21 million, $3 million of which became payable upon execution of the merger agreement, and the remainder of which is contingent upon consummation of the merger.

Interests of Atwood Directors and Executive Officers in the Merger (See page 93)

        Atwood's directors and executive officers have financial interests in the merger that may be different from, or in addition to, those of Atwood shareholders generally. The Atwood Board was aware of these interests and considered them, among other matters, in approving the merger agreement and making its recommendation that Atwood shareholders approve the Atwood Merger Proposal. These interests include the following:

•

The merger agreement provides that Existing Options outstanding immediately prior to the Effective Time will be exchanged for Converted Options to acquire Ensco Class A ordinary shares. All of Atwood's Existing Options previously vested. The Converted Options will otherwise remain subject to the same terms and conditions as the corresponding Atwood options. The number of Ensco Class A ordinary shares subject to the Converted Options will be determined by multiplying the number of shares of Atwood common stock subject to the Existing Options immediately prior to the Effective Time by the exchange ratio, rounded down to the nearest whole share, and the exercise price per share of the Converted Options will equal the per share exercise price of the Existing Options immediately prior to the Effective Time divided by the exchange ratio, rounded up to the nearest whole cent.

•

Pursuant to the applicable Atwood incentive plans, all time-based Atwood RSUs ("Time-Based RSUs") and performance-based Atwood RSUs ("Performance-Based RSUs") held by Atwood's directors and employees shall vest upon the Effective Time. Time-Based RSUs that so vest will be settled through the issuance of Ensco Class A ordinary shares equal to the number of vested Time-Based RSUs multiplied by the exchange ratio. Performance-Based RSUs will vest at the Effective Time at the higher of target level of performance or the amount determined by the compensation committee of the Atwood Board (but not to exceed 200% of target level) and the number of Performance-Based RSUs that vest will be settled through the issuance of a number of Ensco Class A ordinary shares equal to the number of vested Performance-Based RSUs multiplied by the exchange ratio. Accrued cash dividend equivalents on Time-Based RSUs and Performance-Based RSUs will also vest and be cashed out at the same time. Atwood Cash Units will be treated as specified in the applicable award agreement. The Atwood Cash Units are performance vesting awards that will vest in full upon the Effective Time at the higher of target level of performance or the amount determined by the compensation committee of the Atwood Board (up to 200% of target level) and will be paid in cash based on the closing price of Atwood common stock on the last trading day prior to the closing date. Accrued cash dividend equivalents on the Atwood Cash Units will also vest and be cashed out at the same time.



•

Each of Atwood's executive officers is subject to a non-competition and non-solicitation agreement entered into in May 2016 pursuant to which specified time-vesting cash awards and Atwood RSUs were granted. The cash awards and the Atwood RSUs will fully vest and become payable upon the Effective Time, and the Atwood RSUs will be treated as specified above.



•

Executive officers are covered under Atwood's Salary Continuation Plan, formerly named the Executive Life Insurance Plan, which provides for salary continuation to the executive's beneficiary upon the executive's death while employed by Atwood. Payments equal to 2.5 times annual salary are payable in 30 installments or, in the event of death due to accidental causes, payments equal to five times annual salary are payable in 60 installments. If the executive officer terminates employment within 30 months following a change of control, the death benefit is payable if the executive dies during that 30-month period.



•

Each of Atwood's executive officers is subject to a change of control agreement that provides specified severance benefits if the executive officer experiences a qualifying termination of employment within 24 months following a change of control. The benefits include cash severance, 24 months of continued coverage under Atwood's welfare benefit plans and the right to exercise stock options for up to one year following termination.

        Atwood's directors and executive officers are also entitled to continued indemnification/expense advancement and directors' and officers' liability insurance coverage under the merger agreement.

Board of Directors and Executive Officers of Ensco Following the Merger (See page 91)

        The current directors of Ensco are: Paul E. Rowsey, III, Carl Trowell, J. Roderick Clark, Roxanne J. Decyk, Mary E. Francis CBE, C. Christopher Gaut, Gerald W. Haddock, Francis S. Kalman and Keith O. Rattie. At the Effective Time, Ensco will cause two directors currently serving on the Atwood Board, Jack E. Golden and Phil D. Wedemeyer, to be appointed to the Ensco Board and will expand the Ensco Board to the extent necessary in connection with appointing such additional directors. The two additional directors were proposed by Atwood following the execution of the merger agreement and have been mutually agreed upon by Ensco and Atwood. All Ensco directors are elected annually to serve until the next annual meeting and until their successors are elected.

        Ensco's executive officers will remain the same following the merger, and none of Atwood's executive officers are expected to have any executive officer positions with the combined company.

Public Trading Markets (See page 91)

        The Ensco Class A ordinary shares are quoted on the NYSE under the symbol "ESV," and the Atwood common stock is quoted on the NYSE under the symbol "ATW." Upon completion of the merger, the Atwood common stock will be delisted from the NYSE and deregistered under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). The Ensco Class A ordinary shares issuable in the merger will be listed on the NYSE and will be freely transferable under the Securities Act of 1933, as amended (the "Securities Act").

Regulatory Approvals Required for the Merger (See page 92)

        To complete the merger, Ensco and Atwood must make filings with and obtain authorizations, approvals or consents from a number of regulatory authorities. The merger is subject to the requirements of the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (the "HSR Act"). On June 9, 2017, Ensco and Atwood filed a Premerger Notification and Report Form pursuant to the HSR Act with the Antitrust Division of the Department of Justice (the "DOJ") and the Federal Trade Commission (the "FTC"). On June 27, 2017, the DOJ and the FTC granted early termination of the waiting period under the HSR Act. In addition, the new Ensco Class A ordinary shares to be issued to Atwood shareholders must be approved for listing on the NYSE, subject to official notice of issuance.

Expected Timing of the Merger (See page 99)

        Unless Ensco and Atwood agree otherwise, completion of the merger will occur as soon as practicable, but no later than within five business days after the satisfaction or waiver of the conditions set forth in the merger agreement, except for those conditions that are to be satisfied at the closing. The parties expect such conditions to be satisfied in the third calendar quarter of 2017. However, as the merger is subject to regulatory clearance and the satisfaction or waiver of other conditions described in the merger agreement, it is possible that factors outside the control of Ensco and Atwood could result in the merger being completed at a later time or not at all.

Adverse Recommendation Changes (See page 109)

        Subject to the conditions described in this joint proxy statement/prospectus, the merger agreement provides that neither the Ensco Board nor the Atwood Board will:

•

change, qualify, withhold, withdraw or modify, or authorize or publicly propose to change, qualify, withhold, withdraw or modify, in a manner adverse to Atwood or Ensco its recommendation with respect to the Ensco Merger Consideration Proposal or the Atwood Merger Proposal, as applicable;



•

take any formal action or make any recommendation or public statement in connection with a tender offer or exchange offer;



•

adopt, approve or recommend, or publicly propose to adopt, approve, or recommend, to the Ensco shareholders or Atwood shareholders, as applicable, a takeover proposal; or



•

authorize, cause or permit Ensco or Atwood or any of its subsidiaries, as applicable, to enter into any letter of intent, agreement, commitment or agreement in principle with respect to any takeover proposal.

        The taking or failure to take, as applicable, of any of the actions described above is referred to as an "adverse recommendation change." Subject to the conditions described in this joint proxy statement/prospectus, prior to receiving shareholder approval of the Ensco Merger Consideration Proposal or the Atwood Merger Proposal, as applicable, either the Ensco Board or the Atwood Board

may make an adverse recommendation change in response to an event (an "intervening event") that (i) was not known to such board of directors (or the material consequences of which, based on facts known to members of such board of directors as of the date of the merger agreement, were not reasonably foreseeable as of the date of the merger agreement); (ii) becomes known by such board of directors prior to the receipt of shareholder approval; and (iii) does not relate to the receipt, existence or terms of a takeover proposal involving Ensco or Atwood, as applicable. Either the Ensco Board or the Atwood Board may make an adverse recommendation change in response to an intervening event if such board of directors has determined in good faith after consultation with its outside financial advisors and outside legal counsel that the failure to take such action would be inconsistent with its fiduciary duties under applicable law, subject to certain conditions described in this joint proxy statement/prospectus.

Agreement Not to Solicit Other Offers (See page 109)

        Except as expressly permitted by the merger agreement, each party will, and will cause its affiliates, and officers, directors and employees to, and will use reasonable best efforts to cause its agents, financial advisors, investment bankers, attorneys, accountants and other representatives to:

•

immediately cease any ongoing solicitation, discussions or negotiations with any person with respect to a takeover proposal;



•

promptly instruct (to the extent such party has the contractual authority to do so) any person that has executed a confidentiality or non-disclosure agreement within the 24-month period prior to the date of the merger agreement in connection with any takeover proposal to return or destroy all confidential information of such party in its possession; and



•

until the Effective Time or termination of the merger agreement, not:



•

solicit, initiate or knowingly facilitate or knowingly encourage (including by way of furnishing non-public information) any inquiries regarding, or the making of any proposal or offer that constitutes, or could reasonably be expected to lead to, a takeover proposal;



•

engage in, continue or otherwise participate in any discussions or negotiations regarding, or furnishing to any other person any non-public information in connection with or for the purpose of encouraging or facilitating, a takeover proposal; or



•

approve, recommend or enter into, or propose to approve, recommend or enter into, any letter of intent or similar document, agreement, commitment or agreement in principle (whether written or oral, binding or nonbinding) with respect to a takeover proposal, other than as expressly permitted by the merger agreement.

        In addition, neither party will release any third party from or waive or amend any standstill provision or confidentiality provision other than any confidentiality provision the waiver of which would not be reasonably likely to lead to a takeover proposal, and each party will enforce such confidentiality and standstill provisions of any such agreements and take all steps within its power to terminate any waivers previously granted under any such provisions.

Conditions to Completion of the Merger (See page 114)

        Each party's obligation to consummate the merger is conditioned upon the satisfaction (or waiver by such party) at or prior to the completion of the merger of each of the following:

•

the approval of the Atwood Merger Proposal by holders of at least two-thirds of the outstanding Atwood common stock;

•

the approval of the Ensco Merger Consideration Proposal by holders of at least a majority of Ensco Class A ordinary shares cast at the Ensco general meeting;



•

the approval for listing by the NYSE, subject to official notice of issuance, of the Ensco Class A ordinary shares issuable to Atwood shareholders in connection with the merger;



•

the effectiveness of the registration statement of which this joint proxy/prospectus is a part under the Securities Act and no stop order suspending the effectiveness of the registration statement having been issued and no proceedings for that purpose having been initiated or threatened by the SEC;



•

no injunction by any court or other tribunal of competent jurisdiction shall have been entered and shall continue to be in effect and no law shall have been adopted or be effective, in each case that prohibits the completion of the merger;



•

the termination or expiration of any waiting period (and any extension thereof) applicable to the merger under the HSR Act as well as any other approvals that may be required by a competition law authority in any foreign jurisdiction;



•

since the date of the merger agreement, there has not been any change in U.S. tax law that would cause Ensco to be treated as a domestic corporation for U.S. federal income tax purposes;



•

(i) the representations and warranties of the other party shall be true and correct both at and as of the date of the merger agreement and at and as of the completion of the merger as though made at and as of such date, except where such failures to be so true and correct (without regard to "materiality," "material adverse effect" and similar qualifiers contained in such representations and warranties) would not, individually or in the aggregate, have a material adverse effect on the other party, (ii) the representations and warranties of the other party with respect to capitalization shall be true and correct both as of the date of the merger agreement and as of the closing date, except for any de minimis inaccuracies, (iii) there have not been any changes with respect to Ensco that would reasonably be expected to have, individually or in the aggregate, a material adverse effect on Ensco and (iv) there have not been any changes with respect to Atwood that would reasonably be expected to have, individually or in the aggregate, a material adverse effect on Atwood;



•

the performance and compliance, in all material respects, with each and all of the covenants required to be performed with and complied with by the other party pursuant to the merger agreement; and



•

the receipt of a certificate by the chief executive officer, or other senior officer, of the other party, dated as of the closing date, certifying that the two preceding conditions have been satisfied.

Termination of the Merger Agreement (See page 114)

        Generally, the merger agreement may be terminated prior to the completion of the merger, whether before or after the Ensco Merger Consideration Proposal or the Atwood Merger Proposal is approved (as applicable and except as otherwise specified below), as follows:

•

by the mutual written consent of Ensco, Merger Sub and Atwood;



•

by either Ensco or Atwood, if:



•

the merger shall not have been consummated on or prior to February 28, 2018 (the "End Date"); provided, however, that if all conditions of the closing have been satisfied, except for the requirement to receive approval under the HSR Act or certain other governmental

approvals, either Ensco or Atwood may extend the End Date up to, but not beyond, May 29, 2018;

•

an injunction has been entered permanently restraining, enjoining or otherwise prohibiting the consummation of the merger and such injunction has become final and non-appealable; provided, however, that if such injunction was primarily due to the failure of a party to perform its obligations under the merger agreement, then such party may not terminate the merger agreement under this provision;



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the Atwood shareholders have not approved the Atwood Merger Proposal;



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the Ensco shareholders have not approved the Ensco Merger Consideration Proposal; or



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the other party has breached or failed to perform any of its representations, warranties, covenants or other agreements contained in the merger agreement, if such breach or failure of performance occurred and continued to occur on the closing date and would result in the breach or failure of certain conditions set forth in the merger agreement and, by its nature, such breach or failure cannot be cured prior to the End Date;



•

by Atwood, if:



•

the Ensco Board makes an adverse recommendation change or Ensco materially breaches its non-solicitation obligations; or



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Atwood is terminating the merger agreement to enter into a definitive agreement relating to a superior proposal in accordance with the terms of the merger agreement and Atwood pays the Atwood Termination Fee (as defined below);



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by Ensco, if:



•

the Atwood Board makes an adverse recommendation change or Atwood materially breaches its non-solicitation obligations; or



•

Ensco is terminating the merger agreement to enter into a definitive agreement relating to a superior proposal in accordance with the terms of the merger agreement and Ensco pays the Ensco Termination Fee (as defined below).

Termination Fees (See page 116)

        Atwood must pay Ensco a $30 million termination fee (the "Atwood Termination Fee") if:

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(i) (A) Atwood or Ensco terminates the merger agreement because the End Date has passed or the Atwood shareholders have not approved the Atwood Merger Proposal or (B) Ensco terminates the merger agreement because Atwood has materially breached the non-solicitation restriction and (ii) (A) a takeover proposal has been made to Atwood or the Atwood shareholders or any person has publicly announced an intention to make a takeover proposal, (B) such takeover proposal or the intention to make a takeover proposal was publicly disclosed prior to the termination (and remained pending as of the termination) and (C) within twelve months after termination of the merger agreement Atwood has consummated, or entered into a definitive agreement to consummate, a takeover proposal;



•

Ensco terminates the merger agreement because the Atwood Board changes its recommendation in response to an intervening event; or



•

Atwood terminates the merger agreement to accept a superior proposal in accordance with the terms of the merger agreement.

        Ensco must pay Atwood a $50 million termination fee (the "Ensco Termination Fee") if:

•

(i) (A) Atwood or Ensco terminates the merger agreement because the End Date has passed or (B) Atwood terminates the merger agreement because Ensco has materially breached the non-solicitation restriction and (ii) (A) a takeover proposal has been made to Ensco or the Ensco shareholders or any person has publicly announced an intention to make a takeover proposal, (B) such takeover proposal or the intention to make a takeover proposal was publicly disclosed prior to the termination (and remained pending as of the termination) and (C) within twelve months after termination of the merger agreement Ensco has consummated, or entered into a definitive agreement to consummate, a takeover proposal;



•

Atwood or Ensco terminates the merger agreement because the Ensco shareholders do not approve the Ensco Merger Consideration Proposal or the Ensco Board changes its recommendation in response to an intervening event; or



•

Ensco terminates the merger agreement to accept a superior proposal in accordance with the terms of the merger agreement.

Expense Reimbursement (See page 116)

        If the merger agreement is terminated by either party due to the breach by the other party of its representations, warranties and covenants set forth in the merger agreement, then the breaching party will reimburse all reasonable out-of-pocket fees and expenses incurred by the other party in connection with the merger up to $10 million. In addition, Atwood will reimburse Ensco up to $10 million of all reasonable out-of-pocket fees and expenses incurred in connection with the merger in the event that Atwood does not obtain shareholder approval of the Atwood Merger Proposal.

Accounting Treatment of the Merger (See page 92)

        Ensco prepares its financial statements in accordance with generally accepted accounting principles in the United States ("GAAP"). The merger will be accounted for using the acquisition method of accounting with Ensco being considered the acquirer of Atwood for accounting purposes. This means that Ensco will allocate the purchase price to the fair value of Atwood's tangible and intangible assets and liabilities at the acquisition date, with the excess purchase price, if any, being recorded as goodwill, or the excess of the fair value of Atwood's tangible and intangible assets and liabilities at the acquisition date over the purchase price, if any, being recognized in Ensco's earnings. Under the acquisition method of accounting, goodwill is not amortized but is tested for impairment at least annually.

No Appraisal or Dissenters' Rights (See page 91)

        Atwood shareholders who dissent to the merger will not have rights to an appraisal of the fair value of their shares. Under the TBOC, shareholders generally have appraisal rights in the event of a merger or consolidation. However, these appraisal rights are not available if (i) the shares held by the shareholder are part of a class of shares listed on a national securities exchange or held of record by at least 2,000 holders, (ii) the shareholder is not required to accept for his or her shares any consideration that is different than the consideration to be provided to any other holder of shares of the same class held by the shareholder, and (iii) the shareholder is not required to accept any consideration other than shares of a corporation that satisfy the requirements in clause (i) above. Because Ensco Class A ordinary shares are listed on the NYSE, a national securities exchange, and are expected to continue to be so listed following the merger, and because the merger otherwise satisfies the foregoing requirements, Atwood shareholders will not be entitled to appraisal or dissenters' rights in the merger with respect to their shares of Atwood common stock.

Comparison of Shareholder Rights (See page 148)

        Upon completion of the merger, Atwood shareholders will become Ensco shareholders and will have different rights once they become Ensco shareholders due to differences between the governing corporate documents of each entity. These differences are described in detail in the section entitled "Comparison of Rights of Atwood Shareholders and Ensco Shareholders" beginning on page 148.

Litigation Relating to the Merger (See page 92)

        On June 23, 2017, a putative class action lawsuit was filed against Atwood, Atwood's directors, Ensco and Merger Sub. The complaint generally alleges that the directors and Atwood disseminated a false or misleading registration statement which omitted material information regarding the proposed transaction between Ensco and Atwood, in violation of Section 14(a) of the Exchange Act. Specifically, the complaint alleges that Atwood and the directors omitted material information regarding the parties' financial projections, the analysis performed by Goldman Sachs in support of its fairness opinion, the timing and nature of communications regarding post-transaction employment of Atwood's directors and officers, potential conflicts of interest of Goldman Sachs, and whether there were further discussions with another potential acquirer of Atwood following announcement of the merger. The complaint seeks injunctive relief, including to enjoin the merger, rescission or rescissory damages in the event the merger is consummated, and an award of attorneys' fees, in addition to other relief. On June 27, June 29 and June 30, 2017, three additional putative class action lawsuits were filed against Atwood and Atwood's directors. These actions allege violations of Sections 14(a) and 20(a) of the Exchange Act by Atwood and Atwood's directors similar to those alleged in the original complaint discussed above; however, neither Ensco nor Merger Sub is named as a defendant in these actions.

SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF ENSCO

        The following selected historical consolidated financial data for each of the years ended December 31, 2016, 2015, 2014, 2013 and 2012 are derived from Ensco's audited historical consolidated financial statements. Financial data for the six months ended June 30, 2017 and 2016 are derived from Ensco's unaudited consolidated financial statements. These historical results are not necessarily indicative of the future performance of Ensco following completion of the merger.

        You should read the following historical financial data in conjunction with "Management's Discussion and Analysis of Financial Condition and Results of Operations" and the consolidated financial statements and the related notes thereto set forth in Ensco's Annual Report on Form 10-K for the year ended December 31, 2016 and Form 10-Q for the quarterly period ended June 30, 2017, which are incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information."

SELECTED HISTORICAL CONSOLIDATED FINANCIAL DATA OF ATWOOD

        The following selected historical consolidated financial data for each of the fiscal years ended September 30, 2016, 2015, 2014, 2013 and 2012 are derived from Atwood's historical consolidated financial statements. Financial data for the nine months ended June 30, 2017 and 2016 are derived from Atwood's unaudited condensed consolidated financial statements also appearing herein and which, in the opinion of management, include all adjustments, consisting only of normal recurring adjustments, necessary for a fair statement of the results for the unaudited interim periods. These historical results are not necessarily indicative of the future performance of Atwood.

        You should read the following historical financial data in conjunction with "Management's Discussion and Analysis of Financial Condition and Results of Operations" and the consolidated financial statements and the related notes thereto set forth in Atwood's Annual Report on Form 10-K for the fiscal year ended September 30, 2016 and Quarterly Reports on Form 10-Q for the quarterly period ended June 30, 2017 and 2016, respectively, which are incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information."

UNAUDITED COMPARATIVE PER SHARE DATA

        The following table sets forth (i) selected per share information for Ensco on a historical basis for the year ended December 31, 2016 and the six months ended June 30, 2017, (ii) selected per share information for Atwood on a historical basis for the year ended September 30, 2016 and the nine months ended June 30, 2017, (iii) unaudited selected per share information for Ensco on a pro forma basis after giving effect to the merger for the year ended December 31, 2016 and the six months ended June 30, 2017 and (iv) unaudited selected per share information for Atwood on an equivalent pro forma basis based on the exchange ratio of 1.60 Ensco Class A ordinary shares for each share of Atwood common stock for the year ended December 31, 2016 and the six months ended June 30, 2017.

        The pro forma information set forth below, while helpful in illustrating the financial characteristics of the combined company under one set of assumptions, does not reflect the possible impact on the combined company that may result as a consequence of the merger and, accordingly, does not attempt to predict or suggest future results. It also does not necessarily reflect what the historical results of the combined company would have been had our companies been combined during 2016. Upon completion of the merger, the operating results of Atwood will be reflected in the consolidated financial statements of Ensco on a prospective basis. You should read the data with the historical consolidated financial statements and related notes of Ensco and Atwood contained in their Annual Reports on Form 10-K for the years ended December 31, 2016 and September 30, 2016, respectively, and their respective Quarterly Reports on Form 10-Q for the quarter ended June 30, 2017, all of which are incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information."