Jeremy Corbyn has demanded a Commons vote on Theresa May's future after she confirmed a showdown on her Brexit plan would not take place before Christmas.
The Labour leader tabled a long-threatened motion of no confidence in the Prime Minister after she set out the timetable for MPs to pass judgment on her deal with Brussels.
The Prime Minister said the Commons would have the chance to debate her Withdrawal Agreement in the week MPs return to Westminster after Christmas on January 7.
The crucial vote - which was postponed earlier this month to avoid a heavy defeat - will take place the following week.
Mr Corbyn told Mrs May: "A responsible prime minister would, for the good of this country, put this deal before the House this week so we could move on from this Government's disastrous negotiation."
He said it was "unacceptable" to delay the vote and confirmed he was tabling a motion "that this House has no confidence in the Prime Minister".
The wording of the motion, targeted at Mrs May rather than the Government as a whole, would not trigger the process set out under the Fixed-term Parliaments Act which could eventually lead to a general election.
But Labour said it was clearly a confidence motion and should be allocated time for debate by the Government.
A House of Commons spokesman said: "By established convention the Government always accedes to the demand from the Leader of the Opposition to allot a day for the discussion of a motion tabled by the official Opposition which, in the Government's view, would have the effect of testing the confidence of the House.
"It will be for the Government to determine whether to schedule time for debate on this."
Setting out the timetable for the Brexit vote, Mrs May told the Commons: "It is now only just over 14 weeks until the UK leaves the EU and I know many members of this House are concerned that we need to take a decision soon."
The Prime Minister's statement came as:
- Cabinet ministers openly speculated about how to proceed if the deal is rejected
- Brussels appeared to dispute claims that negotiations were continuing over the terms of the deal
- Planning for a no-deal Brexit was being stepped up, with the Cabinet discussing "the next phase in ensuring we are ready for that scenario" on Tuesday
The Prime Minister warned MPs that rejecting her deal would not result in an alternative "miraculously" appearing.
"Avoiding no deal is only possible if we can reach an agreement or if we abandon Brexit entirely," she said.
In a warning to campaigners calling for a second referendum, she said it would "break faith with the British people" and do "irreparable damage to the integrity of our politics".
But one of Mrs May's closest allies said "all options" should remain open if the deal is rejected.
Work and Pensions Secretary Amber Rudd said it would be important to find out the "will of Parliament" on how to proceed, while Business Secretary Greg Clark also appeared to back an indicative vote to find out what - if anything - MPs could support.
Mr Clark told BBC Radio 4's Today programme that if the deal was rejected "we can't just have continuing uncertainty, and I think Parliament should be invited to say what it would agree with".
Ms Rudd told reporters she hoped the Prime Minister's deal would be supported in the vote expected in January, but if not, "we need to find out where the will of Parliament is" and "nothing should be off the table".
Mrs May's official spokesman told a Westminster media briefing there were "no plans" for an indicative vote on a range of Brexit options, but did not definitively rule the option out.
There was confusion over efforts to secure further guarantees over the controversial Northern Irish backstop measure designed to prevent a hard border with Ireland.
Downing Street said talks by officials were continuing "at all levels" to seek further clarification and assurances on the terms of the existing deal - and particularly the nature of the proposed backstop - as agreed at the European Council last week.
But European Commission chief spokesman Margaritis Schinas said no further meetings between the EU and the UK to discuss the Brexit deal are expected.
"The deal that is on the table is the best and the only deal possible - we will not reopen it, it will not be renegotiated," he said.
Meanwhile, Mrs May rejected reports that predecessor David Cameron was giving her advice on handling the Brexit process.
She told the Commons: "He is not giving advice, the last time I spoke to him was when we actually agreed the Withdrawal Agreement, when I spoke to two former prime ministers as a matter of courtesy to indicate to them what had been negotiated with the European Union."
The Prime Minister received support from an unexpected quarter as Brexiteer Jacob Rees-Mogg, ringleader of attempts to oust her last week, congratulated her "on winning the confidence of the Conservatives in this House last week", adding that he wanted to "assure her that she therefore commands my confidence too".
He had previously said that despite seeing off the motion of no confidence by 200 votes to 117 she should resign "as soon as the Queen has a moment in her diary to see her".