Clarke could swing the campaign

But Mr Portillo is far and away the favourite candidate and seems virtually certain to win.

Attention will now focus on what former chancellor Kenneth Clarke decides to do.

There has been widespread speculation he may be persuaded to back Mr Portillo in an attempt to unite the Eurosceptic and Euroenthusiast wings of the party.

If Mr Portillo can pull that deal off - and he is said to have already held talks with Mr Clarke - then he may be unstoppable.

Olive branch

Mr Clarke may yet be persuaded by the left, Euroenthusiast wing of the party to stand himself, but few believe he would win the support of the party as a whole. And the rightwing will also want a credible candidate.

Announcing his candidacy, Mr Portillo appeared to offer a olive branch to the Clarke camp, declaring that, under him, the Conservative party would be more friendly towards Europe.

He did not ditch the anti-single currency policy developed by William Hague, but he spoke about his desire to work with other European centre right parties.

And his friends have suggested he may give members of his shadow cabinet a free hand to campaign on both sides of the argument when there is a referendum on British membership of the euro.

Widdecombe may back Clarke

Meanwhile there was continuing speculation that Ann Widdecombe would run as the standard bearer for the right wing.

But she confused the issue by suggesting she was ready to stand aside in favour of leftwinger Mr Clarke who she clearly believes could command the support of all wings of the party.

That would deprive the right of its obvious candidate and they would then have to find another candidate, possibly Mr Duncan Smith or Mr Davis.

Most still believe, however, that Mr Portillo will manage to do a deal with Mr Clarke, leaving Ms Widdecombe as the likely rightwing front runner.

Forge a deal

Mr Portillo focussed his attention on the need for the party to radically change its tone.

And in a thinly-veiled criticism of Mr Hague's leadership, he insisted the Tories had to become a more inclusive and "moderate" party.

He claimed he would end "yah-boo" politics in favour of a more constructive approach to Labour.

And, while he said everybody in the shadow cabinet had to accept responsibility for the disastrous election campaign, he made it clear he believed it had been misjudged.

He was clearly out to drive home his new image as a moderate, inclusive and unifying force in the party - which is looking at the prospect of a third election defeat in four or five years time.

Hague led Tories to defeat

And if he wins, as is widely expected, his top priority will be to overcome the sense of pessimism that is gripping the party in the wake of its second election humiliation.

There has been speculation that the Tories may tear itself apart during a protracted post-mortem after the election, particularly over the issue of Europe.

Mr Portillo is determined to prevent that and is clearly ready to do whatever he can to forge a deal between the two factions.

The crunch will come when the ballot of Tory MPs is taken. They will decide which two of the candidates will finally be put before the party as a whole.

For the first time, it will be those grassroots members who will have the final say. And, at the moment, Mr Portillo is their first choice.

But a lot can happen in the weeks between then and now. Mr Portillo's private life is certain to come under the spotlight after he admitted to having had homosexual experiences in the past.

And his apparent conversion from hard-line Thatcherite to moderate, inclusive Conservative will also be tested to destruction.

But, as the contest kicked off, few would take bets against Mr Portillo ending up as the next Tory leader.