Prime Minister Theresa May urged restive MPs to think again about rejecting the EU divorce deal, on the eve of a crucial parliamentary vote that could scupper the agreement.
May warned lawmakers that rejecting it risked either a chaotic no-deal scenario or subverting British democracy by blocking Brexit.
"Whatever you may have previously concluded, over these next 24 hours, give this deal a second look," May told MPs in parliament. "No, it is not perfect. And yes, it is a compromise."
Tuesday's vote was meant to take place in December but was postponed, with May facing certain defeat.
She sought assurances from Brussels that would assuage MPs' concerns over the so-called Irish backstop arrangement.
It is the most contentious element which would keep Britain tied to some EU trade rules, with even closer alignment for the province of Northern Ireland, if and until another way was found to avoid border checks with the Republic of Ireland.
European Commission President Jean-Claude Juncker and European Council President Donald Tusk repeated in a letter Monday that they would not reopen the divorce deal, but offered clarifications with "legal value" on the controversial clause.
May admitted their offer fell short of what she wanted, but said MPs now had the clearest assurances they were going to get from the EU — and should support the deal.
She warned MPs of "the consequences of voting against this deal", saying a no-deal Brexit risked breaking up the United Kingdom, while the alternative of blocking Brexit "would be a subversion of our democracy."
But as MPs prepare to vote on Tuesday evening, large numbers of her own Conservative MPs and her Northern Irish allies remain strongly opposed.
In a further setback, government whip Gareth Johnson — a Brexiteer and one of the officials charged with getting MPs to vote for the deal — announced his resignation.
"It is clear this deal would be detrimental to our nation's interests," he said.
In a speech in Stoke, a Brexit-supporting city in the English Midlands, May repeated that the only way to avoid "no deal" was to support her agreement.
"If no deal is as bad as you believe it is, it will be the height of recklessness to do anything else," she said.
But with growing calls to delay Brexit or call a second referendum, she added: "It's now my judgement that a more likely outcome is a paralysis in parliament that risks there being no Brexit."
Assurances with 'legal value'
May signed the divorce deal with other EU leaders in December after 18 months of tough negotiations, but it has faced huge opposition in parliament.
Tusk and Juncker said the EU "does not wish to see the backstop enter into force" and noted that if it was necessary, it would only be temporary.
They promised to work quickly to find alternatives to keep open the border, including using technology, a solution backed by Brexit supporters.
The pair repeated that similar assurances to this nature made at an EU summit in December "have legal value."
The main opposition Labour party, which wants a customs union with Brussels, also dismissed the EU's assurances.
Labour leader Jeremy Corbyn said that since the postponed December vote, May had "completely and utterly failed" to get the EU to bend its position.
He called the deal a "damaging shambles" that was "clearly bad for this country."
Corbyn has promised a vote of no confidence on the back of a government defeat on Tuesday.
If the government loses the confidence vote, parties would have 14 days to find an alternative that had the support of a majority of MPs, or an election would be called.
Speculation is growing in Brussels and London that May could seek an extension to the Article 50 exit process if she loses the vote on Tuesday.
More than 100 cross-party members of the European parliament promised to back a delay to Brexit to allow voters to think again, in a letter to British citizens.
But May said the Brexit date should not be delayed — although she did not rule out the prospect.
"I don't believe that the date of March 29 should be delayed," May told parliament.