By Sara Sjolin, MarketWatch

LONDON (MarketWatch) --Erasing earlier gains, U.K.'s FTSE 100 index ended Monday in negative territory, with GlaxoSmithKline PLC dropping after disappointing test results and the broader market declining in line with other major European indexes.

The London benchmark lost 0.3% to close at 6,598.37, extending its quarterly loss to 2.2%, the first drop since the three-month period ending in June last year.

Helping drag the FTSE lower, shares of GlaxoSmithKline (GSK) lost 1.6% after the drug maker released disappointing results from a late-stage study of Darapladib, a new heart disease drug.

Peer firm AstraZeneca PLC (AZN) lost 1.6%.

More broadly, started to move lower just ahead of the close amid political jitters in France, as Prime Minister Jean-Marc Ayrault resigned after his Socialist Party suffered major losses in local elections over the weekend.

Among shares on the rise in London, some insurance firms rebounded from losses seen on Friday, when the sector was hit hard by a report in The Telegraph of plans of an investigation by the U.K. Financial Conduct Authority into older pensions and savings plans. The FCA on Friday issued a statement to clarify that it wasn't looking at applying current standards retrospectively and said on Monday it launched an independent investigation into a briefing one of its directors gave to the newspaper.

Shares of Resolution Ltd. gained 0.8% and Aviva PLC rose 1.5%.

Shares of Babcock International Group PLC jumped 4.3% after the engineering company said the Nuclear Decommissioning Authority has selected the company's joint venture, Cavendish Fluor Partnership, as the preferred bidder to buy Magnox Ltd. and Research Sites Restoration Ltd., the license companies for 12 U.K. nuclear sites.

Separately, the Bank of England said the number of loan approvals for house purchases was a weaker-than-expected 70,309 in February, compared with an average of 69,563 over the previous six months.

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