Theresa May has topped the first round of voting by Conservative MPs for the party's new leader, with Liam Fox eliminated after finishing last in the race to succeed Prime Minister David Cameron.

The vote among Conservative lawmakers saw interior minister May win 165 votes, with junior energy minister Andrea Leadsom second on 66.

Pensions minister Stephen Crabb has said that he is withdrawing from the race after coming in fourth place with 34 votes.

He said that he is supporting Ms May in the leadership contest, insisting "there is only one candidate" to unite the Tories and form a "cohesive and strong" government.

Brexit campaigner Michael Gove finished third on 48, while Mr Fox was put in last place on 16 votes - ending his leadership bid.

The contest, triggered by Mr Cameron's decision to resign following the 23 June public vote to leave the European Union, is decided by a series of ballots among Conservative lawmakers to whittle the field down to two.

The party's membership will then vote to decide a winner. The result is due by 9 September.

Boris Johnson has thrown his weight behind fellow Leave campaigner Ms Leadsom.

The former London mayor - who saw his own leadership hopes dashed after a devastating personal attack by Michael Gove - said she had "the zap, the drive and the determination" to lead the country.

His intervention came as a significant boost to Ms Leadsom after she was said to have performed poorly in front of Tory MPs at a leadership hustings at Westminster last night.

It was widely seen as an act of revenge against Mr Gove who had been expected to back Mr Johnson for the leadership after campaigning alongside him in the referendum, only to say Mr Johnson was not up to being prime minister.

There was speculation that it could finally scupper Mr Gove's own leadership bid, with many Tories unhappy at the way he treated his erstwhile comrade.

Mr Johnson pointedly praised Ms Leadsom as being "level-headed, kind, trustworthy".

Ahead of the first ballot, a poll by the Conservative Home website of 1,214 party members gave Ms Leadsom a narrow lead with 38%, one point ahead of Ms May on 37%.

In contrast a YouGov poll for The Times of 994 Conservative Party members suggested that if it came to a final round run-off between the two women candidates, Ms May would win by 63% to 31%.

At yesterday's hustings, Ms May strongly defended her insistence that the status of EU nationals living in the UK must be part of the Brexit negotiations after a furious backlash from Tory MPs.

Conservative MPs lined up in the Commons to condemn her comments, accusing Ms May of a "catastrophic error of judgement".

However she took on the issue head-on, insisting the UK Government could not afford to "give away" its negotiating position and that it had to be able to defend the position of British nationals living in the EU.

"It is about a very logical, correct, practical procedure," a spokesman said.

Ms May sought further to burnish her leadership credentials calling for MPs to be given a vote on the renewal of Britain's Trident nuclear deterrent before Parliament breaks for the summer.

Clarke takes aim at Tory contenders

In apparently unguarded remarks broadcast by Sky News, former Conservative chancellor Ken Clarke described leadership hopeful Theresa May as "a bloody difficult woman", and said Michael Gove would take the country to war on three fronts.

He also said Boris Johnson would make a "ridiculous" prime minister and Andrea Leadsom did not really believe in Brexit.

Speaking to former foreign secretary Sir Malcolm Rifkind while still wearing a microphone at the broadcaster's Westminster studio, Mr Clarke described the situation as a "fiasco".

He said he would probably end up voting for Ms May, after giving support to Steve Crabb in the early stages of the contest.

Mr Clarke tells Mr Rifkind: "Theresa's a bloody difficult woman, but you and I worked for Margaret Thatcher."

The senior Tory goes on to say: "I get on all right with her ... and she is good. She's been at the Home Office far too long, so I only know in detail what her views are on the Home Office.

"She doesn't know much about foreign affairs."

He says of Ms Leadsom: "She's not one of the mindless, tiny band of lunatics, who think we can have a sort of glorious economic future outside the single market.

"So long as she understands that she is not to deliver on some of the extremely stupid things that she's been saying."

Both men are disparaging about Mr Gove, with Mr Rifkind saying: "I don't mind who wins as long as Gove comes third ... as long as Gove is not in the final two, I don't mind what happens."

Mr Clarke replies: "I don't think the membership will vote for Gove. I remember being in a discussion once about something we should do in somewhere like Syria or Iraq, and he was so wild, I remember exchanging looks with Liam Fox ... who's much more right wing than me, we were exchanging views, and Liam was raising eyebrows.

"I think with Michael as prime minister we'd go to war with at least three countries at once."

But Mr Clarke did praise the Justice Secretary for ruining Mr Johnson's leadership bid.

"He did us all a favour by getting rid of Boris. The idea of Boris as prime minister is ridiculous," Mr Clarke said.

Mr Clarke also expressed doubts the ex-London mayor and fellow Leave campaigner Ms Leadsom believed in Brexit at all.

"I don't think either Andrea Leadsom or Boris Johnson actually are in favour of leaving the European Union. It was the obvious thing that the voters, ie: Conservative Party members, were going to vote Leave."

Mr Rifkind replied: "I don't think they cared very much either way."

Mr Clarke said he thought he would "wind up voting Theresa", but would support Mr Crabb in the initial stages, even though he does not know what the Work and Pensions Secretary stands for on many issues.