The Conservative leadership candidates have made their final pitches to MPs ahead of the first round of voting.
Mr Clarke said he was in with a 'serious shout' of winning
David Cameron, Ken Clarke, David Davis and Liam Fox each appeared upbeat after their 20-minute slot.
Tory MPs vote on Tuesday and Thursday to decide who goes through to a ballot of all Conservative members.
Mr Cameron is the bookies' favourite but Mr Davis has the most declared backers. Mr Clarke and Dr Fox both believe they can make it through.
'Freedom to roam'
Dr Fox, the first candidate to address MPs, said as he left: "The Tory party will not begin to ever recover properly until we have an intellectual renaissance.
"While the front bench must be bound by collective responsibility, backbenchers must be given the freedom to roam."
Mr Clarke said, as he arrived, said: "I'm in with a serious shout. Especially if I get to the party and the country."
David Cameron 4/7
David Davis 5/2
Liam Fox 8/1
Ken Clarke 14/1
Meanwhile, Mr Cameron said he thought his message had "gone down well".
Mr Davis reported a "very friendly response" from MPs, adding that Mr Clarke might be "disappointed" over his stated wish for a final run-off against Mr Cameron.
Mr Davis has the declared support of 66 MPs, Mr Cameron of 39, Mr Clarke of 25 and Dr Fox of 23. About 40 Tory MPs have yet to declare how they will vote in the secret ballot.
If the MPs vote as they have declared Mr Davis would be guaranteed to make it to the run off - leaving the other three to battle for one spot.
At the hustings, organised by the 1922 Committee of backbenchers, each man delivered a five-minute address, before fielding questions for 15 minutes.
On Monday two more Tory MPs - James Arbuthnot and Andrew Pelling - announced their support for Mr Clarke.
In a joint statement, the pair said the ex-chancellor was the "most experienced and popular candidate with the ability to lead the Conservative Party to victory and to become prime minister".
Geoffrey Cox, MP for Torridge and West Devon, declared his support for Dr Fox, taking his total to 23.
Mr Cameron's campaign was also boosted by the support of four more colleagues - former Cabinet minister Peter Lilley, Maria Miller, Philip Dunne and Robert Wilson.
Mr Lilley, who stood as a leadership candidate in the 1997 contest, said Mr Cameron could make an "outstanding prime minister".
He hoped he would be in the final run off with Mr Davis, who he said had "done a formidable job" as shadow home secretary.
Ms Miller told BBC Radio 4's World at One: "My decision is to support David Cameron, primarily because, all the other candidates are excellent, I particularly like David's ideas, his agenda and the way he is grasping that Britain has changed."
On Sunday, Mr Cameron again refused to answer questions about whether he had used drugs as a student.
"It is time actually to get on with what really matters in this leadership election campaign," he said.
"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."
Mr Lilley said Mr Cameron's reluctance to talk about drugs use showed he "doesn't waive under fire".
Meanwhile, an ICM poll for BBC's Newsnight suggests it would make no difference to two thirds of voters (66%) if the leader of the Conservatives had used cocaine at some point in the past.
The survey suggests that 28% of voters would be less likely to vote Conservative if they knew the party leader had used the drug.
Among those who vote Conservative or would consider doing so, 64% said it would make no difference, while 27% said it would put them off.
The poll also suggests that it would make no difference to 82% of those asked if the leader had used cannabis, while 11% said it was less likely.