Backers of Mr Cameron, who has faced days of intense pressure over his refusal to say whether he has taken hard drugs, privately accused the Davis camp of deliberately stoking the controversy.

The bitter recriminations flew as newspaper photographs appeared of the Shadow Chancellor George Osborne, who is Mr Cameron’s campaign manager, with a “cocaine snorting dominatrix” 12 years ago.

Michael Spencer, one of the Tory party’s most generous donors, told The Times yesterday it had been “blatantly preposterous” of Mr Davis to fuel the row by stating in a Channel 4 interview on Saturday that anyone who had recently taken hard drugs could never lead the Tory party.

Mr Spencer, a Cameron supporter, said: “The Davis campaign has been threatened by David Cameron and this is the response. It is bitterly disappointing. There are bigger issues here. It is a sad, sad response of the Davis team to Cameron’s Blackpool speech.”

Mr Davis, the Shadow Home Secretary, who issued the hard drugs warning only after repeated questioning on Channel 4, was challenged by Jonathan Dimbleby on ITV1 to deny the charge that he was “skilful at dripping poison into the campaign” and then “pretending to pour balm on the wound”. Mr Davis said: “That is simply not true.” Pressed whether his supporters were engaged in black propaganda, he replied: “I have told them, ‘Do not go near this issue’ on a daily basis.

“This has run on because he (Mr Cameron) hasn’t answered it, but he has absolutely got the right not to answer. That’s his call.”

The Times has learnt that Max Clifford, the public relations practitioner, brokered the deal with two newspapers to run the photographs of a youthful Mr Osborne with a former dominatrix called “Mistress Pain”. In the photographs a white substance, which she claimed was cocaine, can be seen on a table in front of them. Mr Osborne, in a statement, denied taking cocaine with the woman, but declined to say whether he had ever taken hard drugs.

Mr Cameron’s team was bouyed last night by evidence that his own support appeared to be holding firm among MPs before tomorrow’s first crucial leadership vote.

Michael Ancram, the deputy leader of the Tory party who is Mr Cameron’s most senior backer, said: “David has made the right response not to answer. If he does, it will start a witch hunt. I still support him. Activists in my constituency have moved strongly behind him. There is no evidence of a switch.”

Kenneth Clarke’s fears of being eliminated in the first round of voting by MPs were allayed when Andrew Lansley, the Shadow Health Secretary, declared his support for the former Chancellor.

Mr Lansley, one of the last heavyweight MPs to declare, said it would be a serious mistake to reject in the first ballot the most popular Tory figure in the country. “With Ken we have been told for years by the electorate, up to and including the past few weeks, that he is the person who they think the Conservative Party should make leader and we have wilfully ignored it,” he told the Dimbleby programme.

Mr Clarke said he hoped that he and Mr Cameron would be the final two in the contest.

Mr Cameron denied yesterday that his campaign had been hurt. “It's time to get on with what really matters in this leadership election campaign, which is to ask which is the candidate best placed to modernise the Conservative Party, to reach out to voters that haven’t supported us before.”

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