Cameron camp believes he has survived drugs onslaught despite Osborne claims

His team was visibly relieved that intensive investigation into his past by journalists from Sunday newspapers had produced no new revelations. Instead, it was his friend and campaign manager George Osborne who came under scrutiny with reports linking him to a prostitute and self-confessed cocaine user. Mr Osborne refused to go into details of his past life, after the appearance of a photograph, taken when he was 22, with his arm around the woman, who was the partner of a close friend. He dismissed the report as a "smear" and "pretty desperate stuff".

In tomorrow's vote Tory MPs will eliminate one of the four candidates battling to succeed Michael Howard. Another ballot on Thursday will then settle which two men who will go before the party's 300,000 members for a head-to-head vote, with the result announced on 6 December.

A party spokesman confirmed yesterday that Mr Osborne had met the woman when she was dating a friend of his, who later became a drug addict, but added: "George Osborne has never had any physical relationship with this woman or anyone connected with her. Nor has he ever taken drugs with her."

Throughout the weekend, Mr Cameron maintained his refusal to answer questions on whether he had taken drugs. Asked by reporters at a teachers' awards event in London, Mr Cameron again stone-walled the drugs issue.

He said: "It is time actually 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, to be an effective opposition, and to win the next election."

These glimpses into the fast-moving lives of the so-called "Notting Hill set" appear not to have damaged Mr Cameron's support, at least among Tory MPs - though their impact on the party members is uncertain.

Mr Cameron's decision not to answer question was endorsed by the former party leader William Hague, who wrote in the News of the World that "if everyone who'd ever taken drugs was denied a top post, some pretty big gaps would open up in the higher ranks of most professions."

He was backed by his main rivals in the leadership contest. David Davis - whose camp had been suspected of encouraging the rumours of drug taking - said Mr Cameron has "absolutely got the right" not to answer these questions.

"David Cameron and George Osborne are both extremely talented young men. Whatever happens in this leadership election they are going to have a fantastic future in the Tory party," he said.

This contrasted with Mr Davis's comment made the day before, when he said that politicians should "give straight answers to straight questions". That opened him to furious criticism from Cameron supporters, who pointed out that the previous year he had sent a briefing note to his senior colleagues urging them not to answer questions about whether they had used cannabis.

Kenneth Clarke, who also raised some eyebrows when he volunteered an announcement that he had never taken cocaine, avoided suggesting that the shadow Education Secretary follow him down the same road. "I strongly advise David to carry on batting the questions away," he said.

Mr Clarke went on to make a "buy one, get one free" offer to the Conservatives after admitting that there was no "ideal" candidate in the tight leadership race. The former chancellor jauntily tried to cash in on his younger rival's success by suggesting that the party needs a leader who is half-Clarke, half-Cameron.

He said that he might serve in a frontbench team led by Mr Cameron, if he was offered "a very senior role" - though he insisted that the best hope for the party would be to have him as leader with, by implication, Mr Cameron in a high-ranking supportive role. "He's probably too young and I'm probably too old. He's got no experience at all and I am loaded with experience. The ideal candidate may be somewhere between the two of us, half the age but half the experience, but he ain't there," Mr Clarke said.

The idea was reinforced by the shadow Health Secretary, Andrew Lansley, who came out yesterday in Mr Clarke's support, after consulting members of his South Cambridgeshire constituency party.

Mr Lansley claimed that what party members wanted was a final run off between Mr Clarke and Mr Cameron, in which he forecast that the former chancellor's "bankable experience, authority and ability" would be decisive.

Mr Clarke claimed that he was "the obvious person to pick" to increase the party's "appeal to the floating voter", and that he had been one of Gordon Brown's "noisiest opponents."

In an appearance on BBC 1's The Politics Show, he went out of his way to praise Mr Cameron as an "intelligent guy" who had run a "professional campaign" - implying that he lacked only experience.

But even if it is correct that the 300,000 party members would like to be presented with a ballot paper containing the names of the oldest and the youngest of the four leadership contenders, the prospect of it happening is remote.

Mr Davis, who has been the front-runner through most of the campaign, is showing signs of recovering from the stormy weather that hit his campaign after a lacklustre performance at the Conservative annual conference.

His team released the names yesterday of 50 constituency party chairman who are publicly backing him. Their constituencies range from safe Conservative seats such as Havant, to Liberal Democrat seats such as Taunton, and "no-go areas" for the Conservatives in the Labour heartlands, such as Hartlepool and East Ham.

Liam Fox, who is vying with Mr Davis for support from the Tory right, added the names of Gerald Howarth and Christopher Fraser to the list of MPs who are publicly supporting him. This brings his total in the Commons to 22, compared with 24 for Mr Clarke, 34 for Mr Cameron and 66 for Mr Davis.