However, during his time as Conservative leader Cameron successfully transformed his party, dismissed at the turn of the century as unelectable, and continued his reforming zeal after winning power in 2010.

He ambitiously led Britain’s first peacetime coalition government in almost a century, averted a break-up of the U.K. in a Scottish independence referendum and overcame social conservatives within his own party to legalize same-sex marriage.

But his final gamble -- to definitively settle the vexatious question of Britain’s place in Europe -- proved to be his undoing.

Cameron had only been a House of Commons lawmaker for four years when he became Conservative party leader in 2005. The then 39-year-old projected youth and dynamism as he pledged to radically overhaul the party that had suffered three successive electoral defeats at the hands of Labour’s Tony Blair.

He called for a “modern compassionate Conservatism” that would inspire a new generation of Conservative voters and recapture the contested center ground of British politics -- much as Blair had done to his own party a decade before.

The alternative to reform, Cameron told a London think-tank a few weeks after his election, is “irrelevance, defeat and failure.” It earned him the epithet “Heir to Blair”.

The Conservatives certainly seemed to change. Cameron repositioned the party as environmentally-friendly and declared they were now sensitive to the country’s social divisions. He promised to match the still-popular Labour government’s spending commitments and vowed not to reduce taxes simply to appease core right-wing voters.

But it was only when Labour, now led by Blair’s successor Gordon Brown, came to be associated with the unemployment and economic downturn caused by the 2007-08 financial crisis that the Conservatives’ popularity soared.

Cameron’s party won the most seats in the 2010 parliamentary election but did not have enough to govern alone.