UK Election 2015: Why David Cameron's political career hangs by a thread

Prime Minister David Cameron is Britain's most popular major party leader and his Conservative Party the most trusted on the economy after helping revive it. But win or lose a knife-edge election this week, his career hangs by a thread. If he loses, it's over instantly. And even if he wins but doesn't secure an overall majority, which opinion polls suggest no party will achieve, he could face a leadership challenge from inside his famously ruthless party before too long.

A descendant of King William IV, Cameron, who came to power in a coalition with the centre-left Liberal Democrats in 2010, says he wants to serve another five-year term "to finish the job" of fixing the economy. He also plans to deliver a European Union membership referendum, which he hopes will cure his country and party of its Eurosceptic angst. But if he doesn't get the Conservatives re-elected on their own, with their first overall majority in the House of Commons for 23 years, he may struggle to serve out a full term. "The Conservatives are very hard-nosed," Greig Baker, a former Conservative staffer who now runs a public affairs firm called Guide said.  "If Cameron can deliver them ministerial red boxes he'll survive the election. But his long term prospects are very bleak. The party has never loved him."

Tim Bale, author of a history of the Conservative Party, says Cameron faces a rough ride from his party even if he keeps the keys to the prime minister's residence, 10 Downing Street. "If he manages to hang onto Number 10 I think they'll forgive him for a couple of weeks," said Bale. "Then it could be difficult."

While polls show voters generally like him personally, Cameron, 48, is the product of an unusually privileged background. The son of a wealthy stockbroker, he attended exclusive boys' boarding school Eton College and Oxford University, and married a woman who traces her ancestry back to another king - Charles II of England. In a country acutely attuned to class, that rubs some Britons up the wrong way. One of his own outspoken lawmakers once called him and his finance minister "two posh boys who don't know the price of milk".

Opposition lawmakers and parts of the media have likened him to "Flashman", a fictional upper class literary anti-hero of the nineteenth century. His strongest boast is that he pulled the economy from a deep downturn to deliver one of the fastest growth rates in the developed world. But real wage growth has only just started to pick up, meaning many voters say the recovery hasn't benefited them.Cameron

'The Nasty Party'

Perhaps Cameron's biggest weakness is that he has failed to quash a perception among some voters that he heads "the nasty party," a term coined by one of his own ministers, Theresa May, more than a decade ago to urge the party to be more inclusive. When Labour's Tony Blair beat them in three straight elections, Conservative insiders feared their failure was a result of a reputation for being indifferent to the poor, close to big business and intolerant of gays and ethnic minorities. 

Cameron, who became Conservative leader in 2005, tried to change that. He started talking about the environment and a "Big Society" where communities would be given more power. In office, he legalised gay marriage, increased foreign aid and appointed Britain's first female Muslim cabinet member. But efforts to make the party seem friendlier were set back by its approach to the budget deficit he inherited - the biggest since World War Two. To reduce it, Cameron pushed through cuts to welfare spending, which the opposition Labour Party said forced the most vulnerable to pay to clean up a mess made by rich bankers.

Cameron says he took other measures to help those on low pay, including lifting the threshold for income tax, raising the minimum wage, overseeing the creation of 2 million new jobs and giving people state help to buy their first homes. But a policy to reduce social housing payments to those in state-funded homes with spare bedrooms, dubbed the "bedroom tax" by Labour, became emblematic of what Cameron's critics called a heartless attitude toward the poor.

Polls showed cutting welfare was nevertheless popular with some voters who resented a class of people portrayed as feckless parasites in a series of TV programmes which held up an unflattering magnifying glass to "Benefits Britain".

'Rebranding U turn'

Under pressure from right-wingers in his party and the rise of the anti-EU UK Independence Party, Cameron shifted the emphasis towards more conventional conservative themes, opening himself up to accusations he was driven by political expediency. As public unease about immigration rose, he toughened his rhetoric and made it harder for non-EU citizens to immigrate.

And though he said he wanted Britain to stay in the European Union, he promised to hold an in-out membership referendum in 2017 if re-elected, alarming sections of the business community who have traditionally allied themselves with the Conservatives but don't want their country to leave the EU. Cameron dropped his nebulous "Big Society" concept. His early enthusiasm for green policies waned, with one aide telling a newspaper he had ordered subordinates to "get rid of all the green crap" - government-imposed fees tacked onto utility bills to subsidise environmental projects.

He became increasingly isolationist on the world stage too. In 2011, he backed involvement in air strikes which toppled Libya's Muammar Gaddafi. Since then, he has presided over a downgrading of Britain's military and diplomatic muscle. A shock defeat in parliament over his desire to conduct air strikes on Syrian government targets in 2013 marked the effective end of his activist foreign policy ambitions.

Would-be successors are already circling. They include May, his interior minister, Boris Johnson, the larger-than-life Mayor of London, George Osborne, Cameron's loyalist finance minister, and Sajid Javid, the culture minister.

On Friday, in a slip rivals said showed he put his own fate before country, Cameron described the election as "career-defining". He was almost certainly right.