Theresa May is heading for emergency Brexit talks with European leaders after leaving Westminster in turmoil.
The prime minister will meet German Chancellor Angela Merkel and Dutch counterpart Mark Rutte on Tuesday to try to obtain reassurances about the UK's exit deal.
It follows her decision to call off a crunch Commons vote on the deal, scheduled for Tuesday, after admitting she faced a "significant" defeat on it.
The move prompted howls of condemnation from the opposition benches as well as a number of Tories.
There is particular opposition to the proposed backstop arrangements for the Irish border, which would see the UK obey EU customs rules after a transition period if a wider trade deal has not been agreed by then.
Many Tory Brexiters who want to see Mrs May replaced as leader have demanded changes to the deal, but European Council president Donald Tusk insisted there was no question of reopening negotiations.
In other developments at Westminster:
- MPs secured an emergency debate on Mrs May's decision to pull the vote
- Opposition leaders accused the prime minister of showing contempt for Parliament over the cancellation of the vote
- Labour leader Jeremy Corbyn faced pressure to force a confidence vote on the Government
Announcing the decision to delay the vote on the Brexit deal, Mrs May told the Commons that if it had gone ahead as planned, the Government would have been defeated by a significant margin.
Alluding to the main point of concern about her deal she said the Northern Ireland backstop is causing "widespread and deep concern."
Speaking on Monday, Mrs May said: "I have listened very carefully to what has been said in this chamber and out of it by Members from all sides.
"From listening to those views it is clear that while there is broad support for key aspects of the deal, on one issue, the Northern Ireland backstop, there remains widespread and deep concern.
"As a result, if we went ahead tomorrow it would be rejected by a significant margin."
She said the Government was also looking at "new ways of empowering the House of Commons" to ensure that any provision for a backstop has "democratic legitimacy and to enable the House to place its own obligations on the Government to ensure that the backstop cannot be in place indefinitely".
International Trade Secretary Liam Fox said it would be difficult to get the Brexit deal through Parliament without reassurances the UK would not be “trapped” in backstop measures ensuring no return to hard border in Ireland.
Referring to Mrs May’s lobbying mission in Europe, Dr Fox told the BBC’s Newsnight: “My colleagues will want to see that their fears of being trapped in a backstop cannot be realised.
“Without the ability to genuinely reassure my colleagues that they could not legally be kept in the backstop against their will, it will be difficult to get this through the House of Commons.”
Dr Fox added: “Can we find a way of giving both sides the reassurances they seek? Are there other ways of achieving the actual backstop itself?
“There is no clear majority in Parliament for anything other than the current deal, with changes to the backstop.
“It seems to me this is the only thing that would be able to get through the House of Commons.
“If we can’t get changes to the backstop that may not be possible. In which case MPs, whether they were Leave or Remain, will have to confront that there is then only one of two options; no Brexit, or no deal.”
EU leaders will meet for a summit on Thursday where Brexit will again be on the agenda after the latest developments.
However Mr Tusk tweeted that they "will not renegotiate the deal, including the backstop".
"But we are ready to discuss how to facilitate UK ratification," he said. "As time is running out, we will also discuss our preparedness for a no-deal scenario."
Meanwhile, Tory former prime minister David Cameron has said he has no regrets about calling the Brexit referendum – despite previously warning that leaving the European Union would be an “act of economic and political self-harm”.