Conservative leadership challenger David Cameron says he is not interested in making "pacts or deals" with any potential rival contender.
Mr Cameron says he is getting 'good feedback' for his ideas
There had been talk of a "dream ticket" with ex-chancellor Ken Clarke.
Asked on BBC Radio about that, he said the two differ "on the very important issue of Europe", adding: "I'm not interested in tickets and deals."
Mr Clarke's pro-European views are blamed for his failure to win in the 1997 or 2001 Tory leadership elections.
In an interview earlier this week Mr Clarke said he could not see the UK adopting the euro for at least 10 years - comments seen as signalling that he is likely to be a leadership contender.
Mr Cameron, who said he will stand for the Tory leadership if people like his ideas and approaches, suggested Europe was too much of a stumbling block for him and Mr Clarke to overcome.
"I have a particular issue, obviously, with Kenneth Clarke in that I have great respect for him but we don't agree about the issue of Europe, which is a very important issue facing the future of this country," he said.
"He believes we should have an ever closer union of European states - and I believe we need a new sort of Europe, much more open and free trading and more flexible and we should be returning some powers to nation states.
"Now that's an honest and open disagreement.
"But I don't think this is about personal ambition - it's about putting forward the right ideas and approaches that I think are right for Britain in 2005.
"If people think you've got the right ideas, then you will win the contest and you'll run the Conservative party. If people don't think you have got the right ideas, then you won't."
He said: "You can do a deal with Mother Theresa, but if you haven't got the right ideas, you are not going to contribute to the future of the Conservative party of the future of the country - and that is what I'm interested in."
But he said he had so far received "good feedback for what I am saying".
Mr Cameron made the comments ahead of a speech to the Foreign Policy Centre in London in which he likened Islamic terrorists to Nazis and warned that failing to confront them would be fatal.
Earlier this week, in an interview with the journal Central Banking, Mr Clarke argued that the euro had failed to improve productivity and efficiency as much as he had hoped.
He said he accepted there was only a remote possibility that Britain would sign up to the single currency in the next decade.
He also reaffirmed his belief that the European Constitution was effectively dead.
That apparent softening of his pro-European views, plus mounting support for him to make a leadership bid, prompted speculation that Mr Clarke should stand on a "dream ticket" with Mr Cameron.
Since Tory leader Michael Howard announced he would step down later this year, a series of potential candidates have been setting out their visions for the party, which has been in opposition since 1997.
Potential candidates also include Liam Fox, David Willetts, Theresa May, Sir Malcolm Rifkind, Andrew Lansley, Tim Yeo and David Davis, who is the bookmakers' favourite.