Britain has been plunged into fresh constitutional chaos after MPs failed to back any of eight options to Theresa May’s twice-rejected Brexit deal.

The dramatic development followed an earlier one when the Prime Minister promised to sacrifice her premiership in a last throw of the dice to help get her withdrawal plan through the House of Commons.

Her decision – to stand down if her Brexit plan is passed by MPs – is aimed at persuading Tory Eurosceptic colleagues to back her deal, possibly within the next 48 hours.

One, Boris Johnson, who emerged smiling from a closed meeting of Tory MPs and peers, swiftly made clear he would now be backing Mrs May’s deal.

But last night the PM’s big gamble appeared not to have paid off as the Democratic Unionists – who prop up the Conservative administration at Westminster – delivered her a major blow when Arlene Foster, their leader, confirmed the Northern Irish party continued to oppose Mrs May’s deal. “We cannot sign up to something that will damage the Union,” she said.

MPs did approve by 441 votes to 105 to changing the deadline to May 22 if a withdrawal agreement is passed this week, or April 12 if it is not.

But a few hours later, the political crisis gripping Westminster showed no sign of abating after MPs took control of the parliamentary agenda but failed to secure a majority on any of eight other options, including a softer Brexit with a customs union, a People’s Vote, revoking Article 50 and a no-deal outcome.

The closest votes were on a customs union, defeated by just eight votes, and a second EU vote, defeated by 27.

Supporters of a softer Brexit pointed out that 264 MPs had voted for a customs union and 268 for a second referendum, which were more than the 249 who had backed Mrs May’s deal.

In the Commons, Stephen Barclay, the Brexit Secretary, said that, with no majority for any of the eight options, MPs should now back Mrs May’s deal “in the national interest”.

“The results of the process this House has gone through today strengthens our view that the deal the Government has negotiated is the best option,” he declared. 

While the Government signalled it would table a motion to have the option of holding a third meaningful vote on Friday – the original exit day – there was no firm decision announced to do so. No 10 has consistently maintained the Government would only hold MV3 if it felt it had a chance of winning it.

If the Government does not successfully get its deal through by the end of the week then, next week, MPs will meet to see if and how it can progress the other options route.

Sir Oliver Letwin, the veteran Tory MP who led the “indicative votes” process, said the results were “disappointing” but he hoped a new round of votes would be held on Monday. 

John Bercow, the Speaker, confirmed he would allow this to take place, which led to shouts of protest from several MPs.

Following the Commons drama, Ian Blackford, the SNP leader, called for a general election.

“I know we didn’t win but we got more votes for the People’s Vote than the Government got for its proposition. It is becoming increasingly clear this House can’t find a way forward. This Government, this Prime Minister, has failed to provide leadership.

“The only thing we should now be doing is going back to the people of the United Kingdom in a general election to end this impasse,” said the Highland MP.

Earlier, at a closed meeting of the Conservatives’ 1922 backbench committee, Mrs May set out a timetable for her resignation.

“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.”

While she gave no specific date, she said she was “prepared to leave this job earlier than I intended to do what is right for our country and our party”.

It is thought Mr Johnson, who in 2018 denounced Mrs May for having “wrapped a suicide vest” around the British constitution and “handed the detonator” to Brussels, will be among several potential leadership candidates in a contest expected in May or June, when others could include Jeremy Hunt, Sajid Javid, Michael Gove, Dominic Raab and Amber Rudd.

In Scotland, Nicola Sturgeon insisted the PM’s announcement did not change the fact that her Brexit deal was a “profoundly bad one”. But the First Minister noted that the prospect of a Brexiter premier in charge “further reinforces” the case for Scottish independence.

Jackson Carlaw, the Scottish Conservatives’ interim leader, praised Mrs May for her “sense of duty and determination”, and her tireless efforts to achieve an orderly exit from the EU.

But he stressed that this stood in stark contrast to Ms Sturgeon and her response. 

“Entirely predictably, the First Minister has used this announcement to make yet another desperate and spurious push for another independence referendum. So much for the national interest; Nicola Sturgeon only has thought for her own,” added Mr Carlaw.

Jeremy Corbyn tweeted: “Theresa May’s pledge to Tory MPs to stand down if they vote for her deal shows once and for all that her chaotic Brexit negotiations have been about party management, not principles or the public interest.”

One Tory MP at the party meeting, George Freeman, the PM’s former policy advisor, quoted her as saying: “I have made many mistakes. I am only human. I beg you, colleagues, vote for the Withdrawal Agreement and I will go.”

He added: “There was silence in the room and it was incredibly sad.”

Leading Brexiter Jacob Rees-Mogg,cChairman of the European Research Group, said: “The Prime Minister was incredibly dignified. Although I was involved in the challenge against her last year, there is never any joy or happiness in somebody’s political career coming to an end.”