Boris Johnson began positioning himself for a possible leadership election within hours of Mrs May’s announcement, declaring he would back the deal at the third attempt, despite previously describing it as a “suicide vest” for the country.
However, both their actions may have been in vain after the DUP said it was still opposed to the deal, making it highly unlikely the government could pass it at the third attempt.
It came as MPs failed to support any alternative plan for leaving the European Union after seizing control of the Brexit process.
Mrs May went before Conservative MPs at a meeting of the 1922 Committee and told her party that if they backed her deal, she would not lead them into the next phase of Brexit negotiations, on the future trade and security relationship with the EU.
“I am prepared to leave this job earlier than I intended in order to do what is right for our country and our party,” she said.
Later, a Downing Street spokesperson said Mrs May would not necessarily resign in the event of her deal being voted down a third time.
Emerging from the meeting of the 1922 Committee, Scottish Secretary David Mundell said: “It’s another day in which Theresa May demonstrates that she puts the national interest before her own personal interest … she believes it’s her duty to deliver Brexit”
George Freeman, the MP who led her policy unit, said Mrs May had “tears not far from her eyes” as she admitted: “I have made many mistakes. I am only human. I beg you, colleagues, vote for the Withdrawal Agreement and I will go.”
Mr Freeman added that “there was silence in the room and it was incredibly sad”.
His colleague Simon Hart said: “There was warm appreciation for the job she has done so far and no celebration.”
But Mr Johnson emerged smiling and went directly to a meeting of the European Research Group (ERG) of Conservative Brexiteers and declared that he would now support the deal. He still faces an uphill struggle in any leadership race, with a poll of Tory members putting him last in a field of likely candidates.
There was a warning to the government that Mr Johnson may not bring enough ERG converts with him.
In an angry address to the same ERG meeting, former Brexit minister Steve Baker is reported to have told colleagues he was “consumed with a ferocious rage” and “could tear this place down and bulldoze it into the river”.
One source in the group told journalists: “There is no way enough votes are coming out of that room to put the withdrawal agreement through.”
Earlier, to a subdued reaction from her MPs, Mrs May told the packed 1922 Committee meeting: “This has been a testing time for our country and our party. We’re nearly there. We’re almost ready to start a new chapter and build that brighter future. But before we can do that, we have to finish the job in hand.”
She continued: “I have heard very clearly the mood of the parliamentary party. I know there is a desire for a new approach – and new leadership – in the second phase of the Brexit negotiations and I won’t stand in the way of that.
“I know some people are worried that if you vote for the Withdrawal Agreement, I will take that as a mandate to rush on into phase two without the debate we need to have. I won’t – I hear what you are saying.”
The Prime Minister concluded: “I ask everyone in this room to back the deal so we can complete our historic duty – to deliver on the decision of the British people and leave the European Union with a smooth and orderly exit.”
The government now has until the end of the day tomorrow until the EU’s offer of a longer extension to Article 50 expires. Ministers prepared to call Parliament to sit tomorrow for a last-minute vote if the DUP change their stance, with MPs of all parties warned by whips not to make travel plans for the weekend.
However, those plans were thrown into fresh chaos after the DUP leader Arlene Foster said the Brexit deal would endanger the Union and did not have her party’s support.
“What we can’t agree to is something that threatens the union, that has a strategic risk to the union,” she said. “For us in the Democratic Unionist Party, the Union will always come first and that has been the issue right from the beginning of all of this.”
A senior government source had told The Scotsman that ministers were expecting at least some of the DUP’s ten MPs to abstain rather than vote against the deal in a third vote. But DUP deputy leader Nigel Dodds said: “The DUP do not abstain on the Union.”
Labour leader Jeremy Corbyn said any new Conservative leader would have to face the country in a general election.
First Minister Nicola Sturgeon said a vote on the deal was “not about Theresa May’s future, but all our futures”.
She said: “If Brexit ends up being forced through on the basis of a deal that no-one supports – indeed, a deal so bad that the PM has to promise to resign to get it through – it will make an already bad project even worse. For Scotland, this raises the prospect of being shackled to a disastrous Brexit driven by a Tory party lurching even further to the right, with a Brexiteer PM in charge – further reinforcing the case for our country taking its future into its own hands.”