Boris Johnson has said Theresa May can stay on as Prime Minister if her Brexit deal is defeated on Tuesday - as long as she returns to Brussels and demands it abandons the Irish border backstop.
The former Foreign Secretary refused to rule out a leadership bid against the Prime Minister, but said she could stay on even if MPs reject her Brexit deal this week.
If defeated in the Commons on Tuesday, he said work to prepare for a no-deal Brexit should begin “in earnest” to convince the EU the UK was “serious”.
Mr Johnson claimed the backstop measure left the UK open to "blackmail" by the European Union.
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He told BBC's Andrew Marr Show: "The real problem with the backstop arrangement is it gives the power to Brussels and to all the other EU member states effectively to blackmail us and to get what they want out of the future trade negotiation.
"It is a diabolical negotiating position."
Asked if he would promise not to stand against the Prime Minister he said: "I will give you an absolute, categorical promise that I will continue to advocate what I think is the most sensible plan."
But he said it was "nonsense" to suggest he had already begun offering fellow Tories jobs in a future administration.
Mr Johnson claimed it would be “relatively easy” to convince the EU to abandon the backstop despite Brussels insisting the deal will not be changed and that the insurance policy to prevent a hard border in Ireland was a crucial component.
“Do not underestimate the deep sense of responsibility I feel for Brexit and everything that has happened, do not underestimate how much I care about this because this is fundamental to our country,” he told Andrew Marr.
“It breaks my heart that after all we have campaigned for that we should consign ourselves to a future in which the EU effectively rules us in many, many respects and yet we have no say round the table in Brussels.
“That is an absurdity and we cannot go down that route. And unfortunately, the current backstop arrangements would commit us to those arrangements.
“We have to change it, it’s a relatively simply job to do. We can have a withdrawal agreement that does not contain the backstop. We can do much, much better than this."
Another former cabinet minister who resigned over Mrs May's Brexit deal, the ex-Work and Pensions Secretary Esther McVey, said she was willing to stand in a leadership election if asked.
"If people asked me, then of course you'd give it serious thought and do it - if people asked me," she told Sky's Ridge on Sunday programme.
"But at the moment I'm looking at who is in papers, who we can get behind but it shouldn't be about the personality, it should be about the country and this deal."
Dominic Raab, the former Brexit Secretary, claimed Brussels recognised the need to time-limit the Irish border backstop before officials took negotiations in "another direction".
Mr Raab said Michel Barnier, the European Union's chief negotiator, told him he understood the backstop "needs to be short" after being challenged over making it finite.
He described the Brexit deal as the "worst of all the alternatives" and said some of the no-deal Brexit warnings issued by the Government are "just not credible".
Speaking to Sophy Ridge, Mr Raab said he suspects the deal will be voted down but could still be "remedied" if the EU is willing to look again at the backstop and that the UK will transition to a free trade agreement.
"I made clear that it had to be time-limited and finite, and Michel Barnier, at one point in one of our meetings, said 'I understand it needs to be short', but I'm afraid after that the technical track for the negotiations took it in another direction and I was very clear with the Prime Minister that we should of stood firm at that point, and that was back in July," Mr Raab said.
"Now I'm not suggesting it's easy to go back. You lose moments in negotiations and you can't just claw them back. What I am suggesting is that there is probably more flexibility than is being suggested and actually we should have taken a robust line back then and we certainly should be taking one now."