Mr Clarke said he had "no intention whatever" of challenging Mr Hague and it was "highly unlikely" he would stand for the leadership under any circumstances.

The short-term electoral consequences and longer term political damage...could be severe

Kenneth Clarke

Writing in The Independent on Sunday, he warned that in-fighting over Europe could doom the party's electoral prospects.

The newspaper also reported that Mr Clarke told a Westminster reception last week he would be ready to stand against party leader William Hague if there were a leadership contest after the next election.

'Witch hunt'

But Mr Clarke, who ran for leadership in 1997 but was defeated by Mr Hague, said later on Sunday: "I categorically deny that I have told anybody on any occasion that I intend to run for leadership of the Conservative Party.

"I have no intention whatever of running for leadership against William Hague. I think it highly unlikely that I will ever run for the leadership of the Conservative Party again."

In Mr Clarke's letter to the newspaper, he accused eurosceptic "zealots" of launching a "witch-hunt" which threatened the whole future of the party.

Former Conservative Party chairman Chris Patten added his voice to Mr Clarke's warning, saying victory for the eurosceptics could end the Tories' chances of ever winning power again.

Mr Patten told BBC1's Breakfast with Frost: "We have got to be a broad church, not a narrow sect. The anti-Europeans had too much of their head in the nineties.

Hague defeated Clarke in the leadership battle of 1997

"They helped to destroy the Conservative government and they have been making the running since."

The chairman also said he supported moves by shadow chancellor Michael Portillo to broaden the Tories' appeal to the electorate.

He said: "Unless you reach out to people, you are in opposition forever."

Tory disapproval

Mr Clarke first voiced his concerns because of moves to deselect the pro-European former minister, Ian Taylor, in his Surrey constituency of Esher and Walton.

Local members are due to meet on Monday to decide whether to drop Mr Taylor, their MP for 13 years, as candidate for the next general election.

The Tory leadership has expressed its disapproval of the petition, insisting Tory MPs should be free to express their individual opinions.

Mr Clarke warned the Esher and Walton meeting "could be a key occasion in determining the future nature of the Conservative Party".

"The short-term electoral consequences and longer term political damage that would flow from attempts made by the more extreme Euro-sceptics to force a narrow nationalism onto our MPs could be very severe," he wrote.

With shadow chancellor Michael Portillo stating he had no intention to run for party leader earlier in the week, it was believed it could leave the door open for Mr Clarke to try again.