Cabinet ministers have been urged to reject Theresa May’s Brexit plan when they gather for a crunch showdown on Wednesday.
Ministers have been briefed one by one on the contents of a draft divorce deal reached by officials from the UK and EU after months of protracted talks.
Further individual briefings are expected on Wednesday ahead of the special meeting of the full Cabinet at 2pm.
Before that Mrs May will face the House of Commons for a potentially tricky session of Prime Minister’s Questions.
The announcement that a draft text had been agreed by officials was met with open hostility from Tory Brexiteers and Mrs May’s Democratic Unionist Party allies, and scepticism from Remain supporters.
Former Brexit secretary David Davis said the UK had reached a “moment of truth” and urged his former colleagues to reject the proposals.
“Cabinet and all Conservative MPs should stand up, be counted and say no to this capitulation,” he said.
Former foreign secretary Boris Johnson urged his ex-Cabinet colleagues to “chuck it out”, warning on the BBC that the proposals made a “nonsense of Brexit”.
Jacob Rees-Mogg, chairman of the influential European Research Group of dozens of Tory MPs, said: “It is a failure of the Government’s negotiating position, it is a failure to deliver on Brexit and it is potentially dividing up the United Kingdom.”
On the BBC’s Newsnight, he said he had not called for a no confidence vote in Mrs May “but there comes a point at which the policy and the individual become so intimately connected that it will be very hard to carry on supporting this policy”.
Asked if he would be writing a letter to the Tory backbench 1922 Committee about Mrs May’s position, he said: “Not in the next 24 hours.”
Ex-Tory leader Iain Duncan Smith suggested Mrs May’s administration could collapse over the deal.
“If the Cabinet agrees it, the party certainly won’t,” he said, and when asked if the Government’s days were numbered, added: “If this is the case almost certainly, yes.”
Jo Johnson, brother of Boris and a Remain-supporter who quit as transport minister over the Government’s approach, suggested that Cabinet ministers were questioning whether they could support the deal.
Asked if there could be further resignations, he told a rally in support of a second referendum: “I talk to many MPs, colleagues in the Cabinet and elsewhere … I know how much they all think deeply about these issues and they are all looking deep into their consciences and thinking whether they can support this deal.”
The special meeting on Wednesday could potentially be a flashpoint for tensions between Brexiteers and Remainers around the Cabinet table, with speculation that Leave-supporting ministers including Penny Mordaunt, Esther McVey and Andrea Leadsom could be prepared to quit if a deal ties the UK too closely to Brussels.
But sources close to Brexiteer ministers played down the prospect of walkouts, with Mrs Leadsom said to have enjoyed a “good discussion” with the Prime Minister.
Chief Whip Julian Smith told reporters: “I am confident that we will get this through Parliament and that we can deliver on what the Prime Minister committed to on delivering Brexit.”
But the challenge of getting a deal through Parliament appears even more difficult for Mrs May than winning the support of her Cabinet.
The 10 DUP MPs, upon whom Mrs May relies for a majority, appear set to reject a deal if it crosses their red lines.
DUP leader Arlene Foster said: “I am heartened by friends of the Union on both sides of the House and across the UK who have pledged to stand with the DUP in opposing a deal which weakens the Union and hands control to Brussels rather than Parliament.”
She added that “these are momentous days and the decisions being taken will have long-lasting ramifications” and pointedly stated that “every individual vote will count” in the Commons.
Scotland’s First Minister Nicola Sturgeon said MPs must not fall for Downing Street “spin” that rejecting the deal means crashing out of the EU and “instead we should take the opportunity to get better options back on the table”.
The deal follows intense negotiation in Brussels, with measures to prevent a hard border on the island of Ireland the main stumbling block.
Irish broadcaster RTE reported that the deal involved one overall “backstop” in the form of a UK-wide customs arrangement – as sought by Mrs May – but with deeper provisions for Northern Ireland on customs and regulations.
The Guardian reported that an independent arbitration committee will judge when a UK-wide customs backstop could be terminated.
There will also be a review in July 2019 six months before the end of the transition period, at which it will be determined how to proceed – a new trade deal, the backstop or an extension to the transition period.
The Daily Telegraph revealed that Attorney General Geoffrey Cox told Cabinet that Northern Ireland will be in a “different regulatory regime” under the customs backstop and subject to EU law and institutions, something that may “cross a line” for the DUP.
Labour leader Jeremy Corbyn said the party would vote against the deal if it failed to meet its tests.
“From what we know of the shambolic handling of these negotiations, this is unlikely to be a good deal for the country,” he said.
But his own approach to Brexit will come under attack from former prime minister Tony Blair on Wednesday.
In a speech in London Mr Blair will lash out at the “abject refusal of the Labour leadership to lead the country out of the Brexit nightmare”.