By Josie Cox, Ewen Chew and Rebecca Howard 

U.K. markets rallied Friday as Prime Minister David Cameron's Conservative Party looked on track to win the U.K. election with a slim parliamentary majority after drawing far stronger support than expected, the British Broadcasting Corp. projected.

The British pound rose 1.5% to $1.5486, according to CQG. Earlier it reached $1.5521, a level last seen in February, from $1.5243 before exit polls late Thursday.

London's FTSE 100--the benchmark equity index of the country's largest companies--was 1.6% higher, spurring gains on the pan-European index.

Shares in banks, utilities and construction companies got a big boost. Economists said that some of the policies of the main opposition Labour Party had been perceived as potentially negative for those sectors.

Shares in Royal Bank of Scotland Group PLC, Lloyds Banking Group PLC and Barclays PLC were all trading between 4% and 7% higher by midmorning, while utility Centrica PLC was up over 7%, making it one of the biggest gainers on the index.

In debt markets, moves were more muted, with the yield on the 10-year U.K. government bond, or gilt, falling around 0.06 percentage point to 1.87%. Yields fall as bond prices rise.

The Conservatives' strong showing is a far cry from the dead heat predicted in months of pre-election surveys, which could have spelled weeks of uncertainty around the country's political future.

"This result is far less complicated than the markets' worst fears," said Bill O'Neill, head of the U.K. investment office at UBS Wealth Management, which has $668 billion in assets under management.

"With certainty will come a renewed confidence from investors in a more stable and transparent policy climate."

Simon Gergel, chief investment officer for U.K. equities at Allianz Global Investors, said that this outcome is therefore good news for the markets.

"Instead of Fallout Friday, today could turn into Frenzied Friday," he said.

The FTSE 100 and the FTSE 250 index of midcap companies--traditionally more exposed to the domestic economy and therefore particularly vulnerable to political jitters--were resilient in the lead-up to the vote.

So far this year, the FTSE 100 is 6.5% higher. The FTSE 250 is up 11.5% in 2015, thanks to a near 3% gain Friday.

Some strategists and investors cautioned that a government led by Mr. Cameron could hurt sterling in the longer term because of his pledge to hold a referendum on whether Britain should stay in the European Union.

Phyllis Papadavid, senior global currency strategist at BNP Paribas, agreed that the "referendum risk" would "haunt the currency at a later stage," but others brushed off those concerns.

"The prospects of a referendum on EU membership shouldn't rattle markets, " said Brian Jacobsen, a chief portfolio strategist at Wells Fargo Asset Management, which oversees approximately $500 billion in assets.

"It is highly unlikely a so-called Brexit--Britain leaving the EU--will occur," he added. "Membership has its privileges and those would be costly to give up."

Write to Josie Cox at josie.cox@wsj.com

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