Although Mr Davis is still expected to top the poll when Tory MPs vote this month, there are growing signs that he could be defeated by Ken Clarke or David Cameron in the decisive ballot among the party's 300,000 members.
Mr Clarke and Mr Cameron outshone Mr Davis in their conference speeches on Tuesday and their supporters are increasingly confident either man would defeat him in the members' ballot. Tory MPs will choose a shortlist of two names, almost certainly Mr Davis and either Mr Clarke or Mr Cameron.
Mr Davis's speech, described as lacklustre by critics, cost him the support of Alan Duncan, the shadow Transport Secretary, who was said to be "depressed" by it. He will switch to Mr Cameron.
Other MPs who publicly endorsed Mr Davis are said to be having second thoughts, and could support another candidate in the ballot without going public.
Five MPs are believed to have defected from the Davis camp to Mr Clarke, and Mr Cameron won the public backing of four MPs yesterday, taking his support to 20 MPs. Some Clarke allies fear that Mr Cameron, the 38-year-old shadow Education Secretary, may be the main beneficiary of Mr Davis's difficulties after Mr Cameron's powerful conference performance turned him into a serious contender.
One key Davis ally said: "We have lost five MPs because of Ken Clarke's speech, not because of David's performance. If we were in a speaking contest, we know he wouldn't win, but he pressed all the right buttons and it went down well." In another headache for Mr Davis, Liam Fox, the shadow Foreign Secretary, won the backing of three more MPs after wooing the Blackpool conference with a populist right-wing speech. Dr Fox may also win the support of other right-wingers after Michael Ancram, the party's deputy leader, said he had decided not to stand and would return to the back benches. Mr Davis shrugged off critics last night, insisting that, with 66 MPs backing him, he still had more support than his four rivals put together. But allies admit he faced a "big test" and needed to prevent a haemorrhage of support because momentum would be a crucial factor in the contest.
Some grassroots members said his speech cast doubts on whether he had the "X factor" to become prime minister. Andrew Cave, from Greenwich, said that all other leadership candidates had more passion than Mr Davis. "I thought it was really lacklustre; he was lacking charisma. Tony Blair and Gordon Brown would eat David Davis for breakfast."
Mr Davis's odds have lengthened from 1-2 to 5-6. The bookmaker William Hill said Mr Cameron had leap-frogged Mr Clarke to become second favourite at 11/4, with Mr Clarke third favourite at 3/1. Dr Fox came down from 16/1 to 8/1 after his speech and Sir Malcolm Rifkind stayed at 50/1.
Clarke supporters say Eurosceptic MPs were plotting to stop him by tactical voting. They accused members of the Bruges Group of discussing tactics to prevent his name going into the ballot of Tory members. They said Mr Davis would not have "a real mandate" unless he defeated Mr Clarke in the run-off. David Curry, a former minister, said: "We don't want MPs voting tactically to stop Ken Clarke getting on the final ballot because I think the party and the country want to see Ken in that final." In the conference closing speech today, Michael Howard will announce his formal resignation. He will stay on as leader until 6 December, when the result of the members' ballot is announced. It may be delayed a day so the new leader does not have to make an instant debut at Prime Minister's questions on 7 December.
Davis: 'Stop apologising and walk tall'
The Tory leadership favourite David Davis returned to a right-wing agenda and won applause for histough words on terrorism, Europe and crime. He told Conservatives to "stop apologising and walk tall".
The shadow Home Secretary won some of his biggest cheers for his support of Trevor Phillips, the chairman of the Commission for Racial Equality, in his call for immigrants to integrate. "We mustn't accept it when people living here can't speak English, or won't subscribe to Britain's democratic values," he said.
He contrasted the action taken by France to expel five Islamic extremists with Britain, where none had been deported since the London bombings on 7 July. "If the French won't tolerate people who pose a danger to their country, why on earth should we?" he said.
However, he warned that the Tories would oppose elements in Labour's anti-terrorist legislation. "You don't defeat terrorism by sacrificing the fundamental freedoms of ordinary citizens," he said.
He also attacked the EU, saying the Tories should take back powers from the European Commission. "If the Conservative Party doesn't stand up for British interests, who will?" he said. "I will."
Mr Davis reassured the party that he would rebuild the NHS and stand up for the poor. He pointed out that he was brought up by a single parent in a tough neighbourhood. "I wasn't born a Conservative," he said, "I chose to be a Conservative."
David Davis, 56
Time: 19 mins 45 seconds
Rounds of Applause: 22
"Walk tall" 1; "Tough on crime" 2; "Power" 6; "Europe" 2
Best joke: Gordon Brown's given up Prudence and taken up with Patience. But his neighbour's wife doesn't want to move.
Style: Action man in a suit, shirt looked too large at the neck, red tie showing he's not a predictable true blue. Dark suitshows he's serious.
Delivery: Straight, what you see is what you get, thumb and fingers punched the air to emphasise point. He is never at ease speaking in public but delivered the key points in a way that connected with his supporters.
Ovation: Three minutes, but walked off stage to hug his wife, Doreen, after two.
Fox: 'Get up off our knees'
Appealing to the national pride of the Conservative faithful, Liam Fox set out a strongly Eurosceptic pitch for the party leadership.
He won a warm reception for a speech which championed the causes of international human rights and mental illness, but pressed the traditional buttons of the Union flag, crime, the family and Europe for the party rank and file. He told them: "Get up off our knees, stop apologising, know what we stand for and set a new agenda."
In a speech appealing to the party's right, he declared that Britain should re-establish pride in its national identity. He wrapped himself in the flag, telling the conference: "When I suggested all schools in Britain should fly the Union flag as a symbol of what unites us, I was told it was racist. By what possible stretch of the meaning of the word could even the most crazed member of the politically correct brigade regard flying your own flag outside your own schools as racist. Let us send them a message: this conference will never be ashamed of the Union flag."
Three newly elected MPs, Stephen Hammond, Stephen Crabb and Brooks Newmark, declared their support for the shadow Foreign Secretary after the speech.
He made veiled attacks on his rivals but added: "We are having a leadership contest but we shouldn't forget our enemies are Labour and the Liberal Democrats. We are all on the same side."
Dr Liam Fox, 44
Time: 23 minutes
Rounds of applause: 24
Buzzwords: "Europe" 9 "Change" 8 "Win" 2 "Flag" 3
Best joke: "I play tennis with David Cameron and we're friends, even though he beats me. I don't intend having him make a habit of it."
Best soundbite: "It's time for this party to get back on its feet and get off its knees."
Style: Grey single-breasted suit, white shirt and blue patterned tie.
Delivery: Stood behind the podium, with a traditional pre-prepared text.
Ovation: Just under two minutes (despite bringing his fiancée on to the stage to take the applause alongside him).
How one duff speech can wreck a political career
David Davis is not the first front-runner in a Tory leadership contest to damage his chances of success with a poor speech. When Prime Minister Harold Macmillan announced his resignation at the 1963 conference, Rab Butler, his deputy, was regarded as a natural successor. Butler was so confident that he moved himself into the prime ministerial suite of hotel rooms vacated by Macmillan. But on the day of his speech Butler, handicapped by a cold, failed to rise to the occasion. Soon afterwards he found himself sidelined as interest gathered around first Lord Hailsham and then around Lord Douglas-Home. Macmillan advised the Queen that Alexander Douglas-Home was the choice of the Tory party's grandees.
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