At least two of Mr Davis's declared list of 65 supporters have hinted to the Clarke camp that they will back Mr Clarke rather than Mr Davis in the secrecy of the polling booth when Tory MPs hold their first ballot a week today. Clarke supporters are now hoping to prise more Davis backers away from the shadow Home Secretary after he lost his position as the bookmakers' favourite to Mr Cameron during last week's Tory conference in Blackpool.
There is concern in the Clarke camp that the rapid advance of the 39-year-old Mr Cameron could cost Mr Clarke, 65, crucial votes and prevent him reaching the shortlist of two chosen by Tory MPs, from which the party's 300,000 grassroots members will elect the new leader. Mr Clarke and Mr Cameron are pitching for the votes of Tory moderates, while Mr Davis, 56, and Liam Fox, 43, have more appeal on the party's right.
The Clarke camp, which has tried to portray Mr Cameron as too inexperienced to become leader, acknowledges that it needs to change tack following his spectacular rise to serious contender status last week.
A prominent Clarke supporter said: "We are not going to win MPs over from David Cameron or Liam Fox. But David Davis's support is soft. Some people regret signing up for him and have given us a nod and a wink. We think we can persuade them and some others to back Ken."
The Clarke team insists the former Chancellor will perform much better when MPs vote than his list of 20 publicly declared backers suggests. Mr Cameron has 27 names, Mr Fox 15 and Sir Malcolm Rifkind seven.
Mr Clarke's backers insists he is on course for the shortlist by picking up votes in later rounds of the contest, including those MPs backing Sir Malcolm in the first round, after which he is expected to be eliminated.
Mr Cameron said: "I have every chance of winning if I get it right. I have had a very good response from Members of Parliament and the public. "
Denying that he was too young to become Prime Minister, he said: "I think what matters most in life is potential. I have had a lot of useful experience." Yesterday he won the backing of Peter Ainsworth, a former member of the Shadow Cabinet, who had been wooed by the Clarke campaign. "I have concluded that David Cameron has the right ideas for the future of the party and country," he said.
But Mr Cameron continued to be dogged by questions about whether he smoked cannabis as a student. In the Commons, two Labour MPs mocked him, one calling him "Cannabis Cameron".
Mr Davis, the shadow Home Secretary, sought to give a "business as usual" message at Home Office questions on the issue of border controls. His advisers are telling him to "keep calm" and not risk a headline-grabbing initiative that could backfire. Campaign managers insist that, despite his bad week in Blackpool, his support is holding firm.Reuse content