The Brexit Party leader Nigel Farage offered British Prime Minister Boris Johnson the possibility of an electoral non-aggression pact if he goes for a no-deal EU exit, but warned that if he tried to fudge Brexit then he would face a battle over every seat at the next election.

"We would put country before party and we would do it every time," Farage said of the scenario in which Johnson goes for a no-deal Brexit but faced an election.

"We would be prepared in those circumstances to help him, to work with him, perhaps, I don't know, in the form of a non-aggression pact at the election," he said.

Farage, who in 2013 piled so much pressure on then Prime Minister David Cameron that he promised an EU referendum, said that unless Johnson went for a no-deal Brexit he would face an electoral challenge in every parliamentary seat.

He said "a clean break Brexit" on October 31 was the most popular option among voters but he questioned whether Johnson could be trusted on Brexit.

Prime Minister Boris Johnson has 68 days to convince the EU to give him a new Brexit deal, with neither side so far willing to compromise on the most contentious issues. If he can't get a deal, he says Britain will leave the bloc anyway.

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Boris Johnson predicts last-minute Brexit deal, says he's prepared

The United Kingdom is heading towards a constitutional crisis at home and a showdown with the EU after Johnson has vowed to leave the bloc without a deal unless it agrees to renegotiate a Brexit divorce.

The EU Withdrawal Agreement, Farage said, was the worst deal in history even without the Irish border backstop. The Brexit Party leader said he suspected Johnson would try to get an amended Withdrawal Agreement passed by the UK parliament.

"There is a better than 50% chance that we'll face a general election in the autumn," Farage said.