British Prime Minister Tony Blair's main opponents gathered yesterday for their annual conference seeking another new leader - a choice that will go a long way to determining their ability to win the next election.

The Conservatives dominated 20th Century Britain under the stewardship of such iconic leaders as Winston Churchill and Margaret Thatcher. But they have been condemned to opposition since a 1997 landslide election brought Mr Blair's Labour to power.

Now the party commonly known as the Tories are seeking their fifth leader in eight years and the campaigning has already begun ahead of today's start to the conference.

Analysts say they must widen their appeal and claw back the political centre ground from Mr Blair to have any hope of winning.

In a bid to do that, frontrunner David Davis, a right-winger, has pledged deep change and vowed not to swerve further right.

"This is an incredibly important leadership election, an incredibly important conference," Mr Davis told BBC Television.

Five candidates have thrown their hats into the ring so far. Mr Davis's main challenger, former finance minister Kenneth Clarke, a household name having held most of the top posts in government unlike his rivals, said only he was truly a centrist.

"I'm rather amused by the fact that... all five candidates are insisting they are centre-ground politicians," Mr Clarke told the Observer newspaper.

Mr Blair has already said he will step down before the next election, probably in favour of his finance minister: Chancellor of the Exchequer Gordon Brown.

That raises a problem for the Conservatives - that voters can opt for Mr Brown feeling they are not voting for Mr Blair, whose backing for war in Iraq has cost him much public support.

Conservative John Major upset the odds to win the 1992 election because the ousting of the increasingly unpopular Margaret Thatcher gave the electorate a fresh face to vote for without switching parties.

But the Conservatives' biggest headache is that changes to the leadership election process, put forward by current leader Michael Howard, have been thrown out by party members.

That means Conservative MPs will whittle down the cast list to two but the final choice will be put to all party members across the country, who are largely ageing and right wing. Tory leaders since Margaret Thatcher have been consistently lampooned in the press as weak, inexperienced and deeply split over Britain's place in Europe.

Mr Major was widely ridiculed as the "grey man", his successor William Hague as an inexperienced and precocious youngster. In 2001, the Conservatives elected Iain Duncan Smith as leader. Neither he nor Mr Hague dented Mr Blair's standing.

Mr Howard's leadership boosted the party's fortunes with a better showing in the May elections, but there were very few, if any, who believed the party could have won.

If the Conservatives again opt for a little-known right-winger, pollsters say the ruling Labour party will almost certainly win the next election, expected in 2009, and make it much tougher for the Tories even to win the one after that.