Theresa May has warned MPs if they vote against her Brexit deal it could lead to Irish reunification and the break-up of the UK, in a last-ditch effort to win support.
With just over 24 hours to go until the Commons votes on her plan, the prime minister also said the chances of Scottish independence would increase if it was rejected.
“I ask what would a no-deal Brexit do to strengthen the hand of those campaigning for Scottish independence, or indeed those demanding a border poll in Northern Ireland. Surely this is the real threat to our Union,” May told the Commons on Monday afternoon.
MPs are widely expected to inflict a heavy defeat on the prime minister tomorrow.
In a sign of the opposition to the deal on the Tory benches, a government whip resigned on Monday in order to vote against it.
The EU tried to help May by insisting it does not want the controversial Northern Irish backstop arrangement to remain in place permanently following Brexit.
May told MPs the backstop – designed to avoid a hard border in Ireland by keeping the UK closely aligned to EU rules – was the only way to get a deal.
“Rejecting the backstop altogether means no-deal,” she said.
The Withdrawal Agreement makes clear that that backstop comes into effect only if no broader deal on future relations can been reached.
Pro-Brexit Tory MPs, worried about being tied to EU rules indefinitely, want the UK to have the power to withdraw from the backstop without EU approval.
But in its letters published this morning, Brussels did not agree to this.
There was also no indication that the EU was ready to contemplate a fixed deadline date for the backstop to be brought to an end, as many MPs demand.
Dominic Raab, the former Brexit secretary, said the assurances from the EU were not enough. “If you want a better Brexit deal, if you want a better Brexit, we do have to as MPs vote down the deal tomorrow,” he told a press conference in London.
DUP deputy leader Nigel Dodds said the letter from the EU “bolsters our concerns”, as it provided no “legally binding assurances”.
Jeremy Corbyn told the Commons that it was clear that May had failed to secure such assurances from Brussels.
He dismissed the joint letter as no more than “warm words and aspirations”, which “categorically” fell short of the legally binding assurances promised by the prime minister.
The Labour leader repeated his demand that May call a general election to break the Brexit deadlock.
Meanwhile, a Downing Street source failed to explicitly rule out May quitting if she loses the vote, saying: “Let’s have the vote and we’ll focus our attention on achieving the right result.”
May’s spokesman said: “The PM has I think been really clear in her determination to want to deliver on the will of the British people.”
The source also suggested May was not yet focused on finding a cross-party solution to the Brexit impasse in parliament.
“What the PM has consistently said is it is possible to pass this deal based on the votes of Conservative MPs and colleagues in the DUP. We are putting every effort into doing that,” the source said.
But in a relatively rare Commons intervention, former Labour leader Ed Miliband urged May to allow MPs of all stripes to decide the future of negotiations if her Brexit deal is voted down.
The former Labour leader said the PM was “totally sincere in her sense of duty”, but explained: “I want to turn her attention to something which she does not want to contemplate - which is defeat tomorrow night.
“And I say to her in the strongest terms the tone that she strikes in the wake of that eventuality will define her legacy to this country.”
Miliband said she should not “succumb to this absurd argument that this is a war between this house and the government, when the government is a servant of this house”.
He added: “And I want to urge her to give this house an open and honest process where it can express its view and she and the government then becomes the servant of this House in the negotiations.”
But May hit back, saying: “The government is the servant of the people, we are demonstrating that we are delivering what the people want in relation to Brexit.”
Meanwhile, the PM faced multiple attacks from Tory opponents of the deal, signalling she had done little to change minds.
Tory former defence minister Mark Francois described the assurances from the EU and May over her Brexit as a “fig leaf and a small fig leaf at that”.
Tory former international trade minister Greg Hands later questioned how good an agreement May’s deal was for the UK.
He said: “Brussels clearly believe this is a great deal for them, why does the Prime Minister, seemingly as enthusiastically, think that this is a great deal for the United Kingdom?”
Tory ex-minister Sir Desmond Swayne meanwhile urged May to simply suspend parliament until Brexit was complete.
“To guarantee Brexit she should prorogue Parliament until April, tempting isn’t it?”
May replied: “He’s trying to tempt me down a road that I don’t think I should go down, but were Parliament to prorogue until April I would be denied the opportunity to be able to see (him) and answer his questions on a regular basis and that would be very sad.”