Interviewed by The Independent, Mr Clarke repeated his statement that Britain would not enter the euro within the next 10 years but dismissed reports he had changed his view on the single currency. He accused "friends and his enemies" of spinning his remarks in August when he ruled out euro entry for ten years.
He said: "I just said it's not on the agenda."
Today's comments by the ex-Chancellor will come as a blow to supporters, who had been hoping to neutralise the euro issue, which cost him the leadership twice before. His remarks are likely to dominate this week's Tory party conference in Blackpool. It will be a "beauty contest" between the leadership hopefuls, and they are already trying to trip each other up before they reach the platform.
The front-runner, David Davis, claimed the support of 66 MPs - one third of the Tory Party in the Commons - enough to guarantee him a place in the final run-off against a challenger. But he had to shrug off a charge by a Clarke supporter that he was too lazy to lead the party.
Mr Davis won the backing of Lady Thatcher, who was reported to have described the Shadow Home Secretary as "excellent" and "doing a good job" in the contest.
While her endorsement may be seen by her critics as the kiss of death, she has anointed three successive leaders John Major, William Hague, and Iain Duncan Smith.
Today Mr Davis will say in a speech to the Tory Bow Group: '"It's time for the Conservative Party to reclaim the banner of progress and optimism.''
Mr Clarke warned MPs not to stop him going through to a final run-off against Mr Davis, saying that the Tory Party was now so hungry for power that he was well ahead of his rivals with party supporters in the constituencies.
Reinforcing the warning to MPs, Lord Howe of Aberavon, the former foreign secretary, said on GMTV: "I think if Ken Clarke were not recognised by the parliamentary party and by the party as a really effective runner in this race, we would lose a great deal more of those voters we've been losing to the Lib Dems.''
However, eurosceptics said Mr Clarke's views on the euro remained the stumbling block to his leadership. Mr Hague said yesterday: "Ken has to show he is sincere about abandoning all the euro nonsense.''
The eurosceptic Tory donor Stuart Wheeler - a supporter of Liam Fox - on ITV's Jonathan Dimbleby programme hinted he might withhold funding for the party under a Clarke leadership. He said Mr Clarke was "definitely not the right person to be our party leader", citing Europe as the main problem.
Mr Davis said on the BBC AM programme that he was "nervous" about getting to the top. He rejected demands by the right-wing Cornerstone group for a commitment to an extreme right wing agenda. "No would-be leader should put himself in hock, as it were, to any particular part of the party. You have got to lead the whole party,'' he said.
David Cameron, 38, the youngest challengers, said he did not think moving to the right would be the answer to the failure to win three elections in a row.
Mr Clarke scoffed at the suggestion Mr Cameron was fighting on the centre-ground, like himself. "He was Michael Howard's right-hand man all the way through to the last election,' he said. "I have never looked on any one of the other three [Davis, Cameron and Fox] as being a centre-ground politician."Reuse content