Who could become Blair's new opponent?

Britain's opposition Conservative Party ousted its embattled leader yesterday after his failure to capitalise on the worst period of Prime Minister Tony Blair's premiership.

Iain Duncan Smith has resigned and cannot stand in the contest to find a new party chief which will now ensue. Following are profiles of the favourites to replace him:

Michael Howard - A cabinet minister in the Conservative government that ruled up to 1997, Howard, 62, is emerging as a front-runner, installed as 11/10 favourite by bookmakers William Hill.

An old-style political bruiser, he has harried Chancellor of the Exchequer Gordon Brown over his tax and spending plans in his role as Treasury spokesman.

Party supporters believe he would be more robust in holding Mr Blair to account over anything from public service improvements to the Iraq war, which most Britons opposed.

But he suffered from a negative public image during his time as a hardline Home Secretary (interior minister) and displays few soft edges.

Kenneth Clarke - The most popular Conservative with the public at large, the rumbustious Clarke is probably stymied by his enthusiastic pro-Europeanism in a party increasingly opposed to the project.

He lost to Duncan Smith in the 2001 leadership vote and is now 63. But his experience is formidable - Clarke served as health secretary, home secretary and finance minister between 1988 and 1997 and has higher ratings than any of his rivals.

Supporters say he may not stand.

Michael Portillo - Championed by Conservative modernisers, the flamboyant former defence secretary was also seen off by Duncan Smith in 2001 and has insisted he won't stand again.

But analysts say he represents the party's best chance of electoral revival and bookmakers make him their third favourite.

His inclusive message - urging the party to welcome ethnic minorities and gay people and adapt to 21st century society - has not resonated well with an ageing rank-and-file membership.

Aged 50, just 20 days younger than Mr Blair, Mr Portillo was unpopular with the public while in government but his image has been transformed by a burgeoning media career and a rare glimmer of self-deprecation. Old-style rightists were put off by an admission of homosexual experience in his student days.

David Davis - A relative unknown, Davis, 54, is sure to stand. He served as Minister for Europe under Blair's predecessor as prime minister, John Major, but has a low public profile.

Demoted by Duncan Smith last year, there is little love lost between the two.

Oliver Letwin - The party's home affairs spokesman, 47-year-old Letwin is thoughtful and often liberal in his approach. He is also recognised as a genuine intellect but may have too unworldly an image to become leader.

Like Mr Portillo, Mr Letwin has denied he would stand and has a habit of speaking honestly - maybe too honestly. But he may agree to be a deputy to one of the frontrunners.

During the last election, he caused the Conservatives huge trouble by declaring that they would cut taxes by up to £20 billion.

Others - If Mr Portillo does not stand, the modernisers may look to industry spokesman and former minister Tim Yeo but his low profile means he cannot realistically expect to win.

Aristocratic foreign affairs spokesman Michael Ancram may run as he did in 2001. Then, he came last of the five candidates.