By Guy Faulconbridge
BIRMINGHAM, England (Reuters) - Even Prime Minister David Cameron sounds unsure he can win the next election.
Grappling with a stagnant economy and upstaged lately by the boisterous mayor of London, a former schoolmate who seems to want his job, Cameron faces a divided Conservative Party whose members are worried they face electoral defeat in 2015.
His gamble on the return of economic growth has so far failed, a fact bluntly underlined by the International Monetary Fund's downgrade of Britain's growth forecasts on Tuesday, just a day before his annual speech to Conservative activists.
So he spent the morning of his 46th birthday explaining to reporters why even the fiscally orthodox IMF has told Britain it may have to defer spending cuts Cameron has said are vital - and why he felt he still had a chance of winning the next election.
"At this conference there is a sense that we can win the 2015 general election outright if we focus on the big questions," the prime minister told the BBC on the sidelines of the annual party conference in Birmingham.
"It's about growth, it's about dealing with debt and the deficit and it's also about unlocking aspiration."
But in the bars and debating halls at the conference, whose slogan was "Britain Can Deliver", there was deep unease about whether Cameron can deliver victory - let alone the absolute majority that eluded him in 2010 when he only ousted Labour by entering into coalition with the small Liberal Democrat party.
The Conservatives now trail Labour by 10 percentage points in polls; a poorly presented budget and a botched rail franchise tender have prompted complaints of government incompetence.
Though few in the party think it realistic to imagine a change of leader before the next election - despite much talk this week of the populist charms of London mayor Boris Johnson - Cameron's grip on power faces a huge challenge come that vote.
"For David Cameron to lead the Tories to outright victory at the next election he has got to boost the Tory vote by 5 percentage points compared with the last election," said Peter Kellner, president of the YouGov pollster.
"No governing party has achieved that for more than 150 years," he added. "Given Britain's economic problems and public spending cuts, to achieve this would be utterly extraordinary."
The election of May 2015 is almost certain to be decided on the health of the economy - and the government is well behind its own targets for reducing the budget deficit and the IMF forecast the economy would contract by 0.4 percent this year.
Supporters point to the IMF forecast that the $2.5 trillion economy will grow by 1.1 percent next year and say that Cameron and his finance minister, George Osborne, cannot soften their austerity program for fear of spooking bond investors.
But a cut in income tax this year for the wealthiest Britons has allowed Labour on the left to portray the Conservatives as a party ruling for the privileged, a charge sharpened by Cameron's own privileged background and education at Eton and Oxford.
"We have to show we are not just helping our rich friends but that we are on the side of the strivers, the working man," said Robert Halfon, a Conservative member of parliament for an industrial town near London.
"A lot of it we are doing already, but we have not communicated it as well as we might."
While the economy remains his biggest problem, Cameron and his advisers have so far failed to enthuse voters, or many activists, with his own brand of Conservatism.
That is partly explained by Cameron's delicate job of balancing his Liberal Democrat coalition partners with the right wing of his own party, which wants him to be more resolute.
"Cameron is still trying to be all things to everybody," said Charles Moore, a former editor of the Daily Telegraph and biographer of former Conservative leader Margaret Thatcher.
But, he argued, the prime minister could do more to improve his appeal, despite his constraining alliances: "He needs to make more of a virtue of his cutting approach - being more direct and visionary: cutting not just for money but to get a better society if you reform welfare, so a political message."
That lack of directness contrasts with Johnson, a former journalist with a public persona founded on self-deprecating humor; he received a hero's welcome at the conference and gave Cameron pointed advice on how to win the next election.
Johnson's allies say he would like to be leader; though he has been scrupulously loyal to Cameron in public, he pointedly avoided a straight answer to a question on his ambitions during a radio interview on Tuesday.
Cameron used the conference to strike a tougher tone on welfare and raised the possibility of a referendum on Britain's ties with the European Union - both areas where rightwingers want him to take a less consensual approach.
But for the former public relations executive who was feted by his party for taking it back into government after 13 years of Labour rule, Cameron still fears revisiting those long years in opposition when one leading Conservative famously bemoaned its image as a "nasty party" of unelectable right-wing zealots.
"He is worried about the contaminated brand, about being the 'nasty party'," said Moore. "And I think that holds him back."
(Reporting by Guy Faulconbridge; Editing by Alastair Macdonald)