Boris Johnson, the bookies' favourite to replace Theresa May as British prime minister, has threatened to refuse to pay a 39 billion pounds ($71 billion) Brexit divorce bill to the European Union.

Key points: The Conservative Party is expected to name its new leader in late July

The Conservative Party is expected to name its new leader in late July Mr Johnson vowed to take Britain out of the EU by the October 31 deadline

Mr Johnson vowed to take Britain out of the EU by the October 31 deadline Mrs May will serve as caretaker leader until a new prime minister is chosen

Mrs May resigned as Conservative Party leader on Friday after politicians, including fellow Conservatives like Mr Johnson, repeatedly voted down her deal with the EU.

She is serving as a caretaker leader until a new prime minister is chosen and moves into 10 Downing Street.

Mr Johnson told the Sunday Times that if he succeeded Mrs May, he would refuse to pay unless the EU offered a better withdrawal agreement than the one currently on the table.

As it stands, the UK will have to continue contributing to the EU budget, as if it was still part of the bloc, until next year.

The UK will also be liable for outstanding commitments to projects that go beyond 2020.

Mr Johnson quit as the foreign secretary in Mrs May's Cabinet last July over her approach to Brexit.

The race to replace her as Tory leader — and in turn the head of the British Government — officially begins on Monday, local time.

Nominations close in the afternoon, and the party expects to name its new leader in late July.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 4 seconds 2 m 4 s Theresa May breaks down after announcing her resignation as Prime Minister. (Image: Reuters)

Mr Johnson, 54, who also served as London's mayor, has emerged as the early front-runner in a crowded field.

A hard-line Brexit advocate, he vows to take Britain out of the EU by the deadline that was pushed back to October 31 from March 29 even if there is no deal with the EU on withdrawal terms in place.

In the interview with the Sunday Times, Mr Johnson described himself as the only contender who could triumph over the Labour Party led by Jeremy Corbyn, and Nigel Farage's Brexit Party.

He and other Conservatives vying to lead the party insist they can get better terms from EU leaders in Brussels than the ones Mrs May agreed to and was unable to push through Parliament.

But EU officials have said they are not willing to change the terms of the deal reached with Mrs May.

Michael Gove is among a large field of candidates vying for Conservative Party leadership. ( Reuters: Peter Nicholls )

One of Mr Johnson's main rivals for the post, Environment Secretary Michael Gove, continued to be sidetracked on the weekend by questions about his acknowledged cocaine use when he was a youthful journalist.

He told the BBC on Sunday that he was "fortunate" not to have gone to prison.

He said he was "very, very aware" of the damage drugs could cause.

AP/ABC