Former chancellor Ken Clarke is to make a third attempt to win the leadership of the Conservative Party.
Ken Clarke has wide experience as a minister
He has announced his candidacy in the Daily Mail newspaper.
The Rushcliffe MP's pro-euro views were blamed for his defeats in 1997 and 2001, but he says his enthusiasm for UK euro membership has now cooled.
Sir Malcolm Rifkind, who intends to stand, welcomed the news. Colleague Tim Yeo said Mr Clarke, 65, would be a match for Gordon Brown and Tony Blair.
Announcing his intention to stand, Mr Clarke told the Daily Mail: "I am determined that Britain should be governed better than it has been under New Labour.
"I am horrified by a government run on a basis of spin. The political health of Britain has deteriorated very sharply. The Conservative Party must do something about it, and I am the man to do it."
Mr Clarke lost out on the leadership to William Hague in a vote of MPs in 1997 and in 2001 he came second to Iain Duncan Smith, in a run-off decided by grass roots Tories.
Current Tory leader Michael Howard announced his intention to stand down before the end of the year following May's general election defeat.
Mr Clarke has been dropping heavy hints all summer about his intention to run for the leadership, said BBC political correspondent Reeta Chakrabarti.
He is one of the party's most senior and experienced figures - he also held the health, home and education secretary of state posts.
Mr Clarke is expected to seek to benefit from being one of the few Tory MPs to have opposed the Iraq war.
His potential rivals include shadow cabinet ministers David Davis, David Cameron, Liam Fox, Andrew Lansley, Theresa May and David Willetts.
Former foreign secretary Sir Malcolm said Mr Clarke's challenge would not change his intention to stand.
He said: "I think it's important the Conservative Party should have the broadest spectrum of choice when they come to take a decision about who the leader should be.
"There are some issues about which [Ken and I] agree, but there are some on which we disagree - the most important being the European Union."
Mr Yeo, who pulled out of the leadership race at the weekend, said Mr Clarke would help the party take on Labour and force lesser candidates to withdraw.
He told the BBC: "It does mean the one person in the Conservative Party that even his enemies would acknowledge is an equal match for Gordon Brown or Tony Blair will be actually available to become leader."
Sir Malcolm Rifkind was foreign secretary under John Major
A spokesman for Tory leadership rival David Cameron said: "We still believe David Cameron will comfortably beat him in the early rounds of the leadership election.
"Those loyal friends of Clarke will then transfer their support to David in the final run-off, leaving it as a fight between him and David Davis."
Mr Clarke did not challenge Mr Howard for the post, joking that coming second in Tory leadership races was one habit he was giving up.
But earlier this summer he said he wanted to see if the Tories were "leadable" and prepared to be a socially liberal, centre-right party based around a belief in the free market.
He warned the party was "in danger of becoming a natural party of opposition" and said Labour's Gordon Brown - widely thought to be the prime-minister-in-waiting - would "not be easy to beat".
Mr Clarke's critics argue that he is too old for the job and reluctant to change his mind on key issues.
Some also oppose his involvement in selling cigarettes - he is non-executive deputy chairman of British American Tobacco.
The rules for the leadership contest have yet to be fixed.
MPs want the final say to return to them, with grass roots party members consulted only on their preference.
That proposed new system will go to a vote at a convention of local branch chairman and other Tory figures at the end of September.
All the potential leadership candidates will have a chance to speak from the platform at the Conservatives' annual conference in Blackpool in early October.
Nominations for the contest would be likely to open the following week, with the new leader in place by mid-November.