Prime minister will put only withdrawal agreement to a vote on Friday – but it remains unlikely to pass

Theresa May will put only half of her Brexit deal to a vote on Friday, in a final desperate attempt to secure MPs’ support as senior cabinet ministers made clear she must leave No 10 very soon, whatever happens.

On the day Britain was originally meant to leave the EU – something May had promised would happen more than 100 times – the prime minister will put only the withdrawal agreement to a vote, having promised to step aside if the MPs give her their approval.

No 10 is hoping that some Labour MPs could back the withdrawal agreement severing the UK’s membership of the EU, without the political declaration governing Britain’s future relationship with Brussels.

However, it remains extremely unlikely to pass as Labour said it would never vote for a “blindfold Brexit”, while around 30 Eurosceptic Tories and the 10 Democratic Unionist MPs are also holding out against it.

MPs will be warned that failure to back the withdrawal agreement this time will lead to a long extension that requires participation in European parliament elections or crashing out without a deal on 12 April.

MPs who support a soft Brexit are meanwhile working on a new round of votes on the alternatives on Monday, including a compromise that could combine the support of those MPs who voted for a customs union, for Labour’s Brexit plan and for the Norway-style option dubbed “common market 2.0”.

With European leaders sceptical that such efforts will be successful, the EU’s chief negotiator Michel Barnier told diplomats on Thursday that a no deal was now “the most plausible outcome” and ordered work to begin on wargaming the bloc’s response.

No 10 insists that it can still make progress, arguing that passing the withdrawal agreement alone will allow the UK to avoid a cliff-edge Brexit on 12 April and secure another five weeks to renegotiate the political declaration in order win support for the deal in its entirety.

This is because the EU has said the UK will have to leave on 12 April if no deal is passed, but would grant an extension to 22 May if the withdrawal agreement goes through.

But Labour has repeatedly said it is opposed to this plan. After Jeremy Corbyn held a 20-minute call with the prime minister, a spokesperson said: “Jeremy made clear Labour will not agree a blindfold Brexit to force through Theresa May’s damaging deal, which would leave the next Tory party leader free to rip up essential rights and protections and undermine jobs and living standards.”

With the deal looking all but dead without the support of the DUP, there are fears among some ministers and MPs that May could try to cling on and put her deal to the country in a general election if it does not win support. They worry that a futile version of the withdrawal deal is being put to MPs in order for the Conservatives to say at an election that Labour refused to pass even the most basic part of the agreement to leave the EU.

MPs believe some of May’s advisers are pushing the option of an election, but cabinet sources have told the Guardian this option would not be acceptable and that the prime minister’s position was the same whether or not she gets her deal through.

One cabinet minister told the Guardian: “Now the prime minister has said she is going, there is no point in hanging around indefinitely having said that.” The minister also poured cold water on claims that there will be a general election, pointing to the Fixed-term Parliaments Act.

“That is pre-2010 speak. It is not in the PM’s gift to decide that there is a general election. It is in parliament’s gift. I doubt there is a majority in parliament for holding a general election.”

Another cabinet source said: “Now she has said she is going, she will have to go whether she gets the deal through next week or not, and will have to set a timetable. No one can say this publicly because she still commands some sympathy. But there is no point waiting when power is draining away.”

A source in one of the leadership campaigns to replace May also said: “She has got to go regardless. She has fired the starting gun and there is no going back. She cannot carry on and have an election. All her credibility is gone.”

Quick guide The withdrawal agreement and political declaration explained Show Hide What is the withdrawal agreement? This is the agreement that covers the £39bn divorce payment from the UK to the EU, the rights of non-Britons in the UK and of British citizens in other EU countries, and the backstop policy relating to the border between Northern Ireland and the Republic of Ireland. It is a legally binding document and has to be passed by the British and the European parliaments in order for the UK to leave the EU with a deal.

What is the political declaration? This is the joint declaration drawn up with the European Union about what the post-Brexit relationship between the EU and the UK would look like. This is not legally binding and was intended to form the basis of trade talks. Why has the government split them? Sources close to the government say they have split the agreements so that Britain can leave the EU on 22 May without the more contentious political declaration having been passed.

The deadlock in parliament has led many to believe that a general election is increasingly likely but there would be pressure from many MPs to make sure a new leader is in place before any contest is called.

MPs have been called in on Friday, which was meant to be a non-sitting day, in order to vote on the Withdrawal Act. But even No 10 does not appear confident of it passing, given that talks with the DUP appeared to have been shelved on Thursday.

Play Video 0:46 Is this minister's sweary response where we've got to on Brexit? – video

It also acknowledges that the UK cannot legally leave the EU without getting approval from MPs for both the withdrawal agreement and the political declaration.

Making the case for the vote, Geoffrey Cox, the attorney general, said: “When the house listens to the rationale behind it, when it hears the full context of it, I’m sure the house will accept it is not only perfectly lawful, perfectly sensible and is designed to give this house an opportunity of availing itself of a right the European Union has given to us to avail ourselves of an extension until 22 May.

“The view of the government is simply we could not let the time limit expire at 11pm tomorrow, of allowing this house the opportunity of availing itself of that right. It is perfectly reasonable and it is perfectly lawful.”

May’s de facto deputy, David Lidington, also urged MPs to back the withdrawal agreement irrespective of their opinions about the latter.

“If you believe in delivering the referendum result by leaving the EU with a deal then it is necessary to back the withdrawal agreement,” he told the British Chambers of Commerce conference in London.

What could happen if May’s Brexit deal is voted down again? Read more

“Whether a particular MP wants the final destination to look like Norway or look like Canada or look like the proposals in the Chequers white paper, the starting point is the withdrawal agreement itself.”

But Keir Starmer, the shadow Brexit secretary, warned his party’s own MPs not to fall for the government’s pleas to back the withdrawal agreement only, saying the likely Tory leadership contest meant it could be a “Boris Johnson Brexit, a Jacob Rees-Mogg Brexit, or a Michael Gove Brexit”.

He added: “If the prime minister tries to separate the withdrawal agreement and the political declaration altogether, that only makes matters worse. We would be leaving the EU, but with absolutely no idea where we are heading. That cannot be acceptable and Labour will not vote for it.”