There is an all-out war over Theresa May's Brexit deal which faces delay or humiliating defeat on Tuesday

REUTERS/Henry Nicholls

UK prime minister Theresa May.

• There's a big risk that a Parliamentary vote on UK prime minister Theresa May's Brexit deal won't happen on Tuesday.
• The Sunday Times reported that May will return to Brussels to try and renegotiate the most thorny aspect of her deal, the Irish backstop.
• The official line is that the vote will still happen.
• But senior Conservatives have said the deal in its current form is unacceptable, and May risks a collapse in government if she loses on Tuesday.
• Former Conservative minister Esther McVey told Sky News that May couldn't stay as leader if she loses.

An all-out political war has broken out ahead of the Parliamentary vote on UK prime minister Theresa May's Brexit deal on Tuesday.

MPs are scheduled to vote on December 11 on May's plan for a post-Brexit UK, agreed after months of talks with Brussels.

But there are conflicting accounts about whether the vote will go ahead on Tuesday, with The Sunday Times reporting that May intends to return to Brussels next week to negotiate a better deal. It is thought that MPs will overwhelmingly vote against May's deal, raising questions about her future as prime minister.

The report comes after a senior Conservative politician, Sir Graham Brady, publicly warned that the vote could be delayed, thanks to disagreement over a controversial aspect of the deal: the Irish backstop.

Read more: Here's why the Brexit 'backstop' is now the most important issue facing Britain

But Brexit secretary Stephen Barclay defended the current deal and said on Sunday the vote would go ahead on Tuesday as planned. Speaking to the BBC's Andrew Marr, Barclay said: "The vote is going ahead, and that's because it's a good deal, the only deal. We've got the vote on Tuesday, and there is still two full days of debate."

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Former foreign secretary Boris Johnson said the Irish backstop was "an absurdity."

Former foreign secretary Boris Johnson, thought to be eyeing May's job, demurred. Also speaking to the BBC, he said May had to return to Brussels and implied the current deal was unacceptable.

He said: "If the prime minister is able to go back to Brussels next week and say, 'I'm afraid that the Irish backstop solution that you have come up with is very unpopular not just with the country but also with the house of Commons'.... then I think.... they will listen.

"What they want is the best possible deal with the UK."

Johnson added that the current backstop arrangement, which would lead to Northern Ireland being aligned to some EU rules, was "an absurdity."

"We can have a withdrawal agreement that does not contain the backstop," he said.

Former Conservative minister Esther McVey likewise piled in on Sunday, telling Sky News that it would be "very difficult" for May to remain leader if she loses Tuesday's vote. McVey refused to rule out a leadership bid.

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Former pensions secretary Esther McVey.

May's position appears to be precarious. If, as is likely, she loses the vote on Tuesday, she may face a leadership challenge, or potentially even step down. She may call a second referendum or a general election, though both would be desperate rolls of the dice.

May appeared to rule out this latter option in an interview with the Mail on Sunday, with a stark warning against Labour leader Jeremy Corbyn.

She said: "We have a leader of the Opposition who thinks of nothing but attempting to bring about a General Election, no matter what the cost to the country. As someone who cares passionately about my country and my party, I believe Jeremy Corbyn getting his hands on power is a risk we cannot afford to take."