MPs will vote on Theresa May’s Brexit deal later after she secured “legally binding” changes to it following last-minute talks with the EU in Strasbourg.
The PM said the changes meant the Irish backstop – the insurance policy designed to avoid a hard border in Ireland – could not “become permanent”.
At a press conference with European Commission president Jean-Claude Juncker, Mrs May said she had delivered what Parliament asked her to do.
But Labour said the talks had failed.
Speaking alongside Mrs May in Strasbourg, Mr Juncker warned if the deal was voted down, there would be “no third chance”.
Two documents were agreed after Mrs May flew to the European Parliament on Monday with Brexit Secretary Steve Barclay for last-minute talks with Mr Juncker and EU chief Brexit negotiator Michel Barnier.
The first is a “joint legally binding instrument”on the withdrawal agreement which the UK could use to start a “formal dispute” against the EU if it tried to keep the UK tied into the backstop indefinitely.
The other is a joint statement about the UK and EU’s future relationship which commits to replacing the backstop with an alternative by December 2020.
The legal view of the changes taken by Attorney General Geoffrey Cox is likely to be an important factor in the lead-up to the Commons vote.
Mrs May is expected to chair a cabinet meeting on Tuesday morning before the motion is debated in the Commons in the afternoon and votes are held in the evening.
After talks with Mr Juncker, the prime minister said she “passionately believed” her Brexit deal addressed concerns raised by MPs.
Some fear the backstop would keep the UK in a customs arrangement with the EU indefinitely.
“MPs were clear that legal changes were needed to the backstop. Today we have secured legal changes,” she said.
“Now is the time to come together to back this improved Brexit deal and deliver on the instruction of the British people.”
The Democratic Unionist Party, whose support Mrs May relies on in the Commons, said it would be “scrutinising the text line by line” before deciding whether to back the deal.
Last time Mrs May’s withdrawal agreement was put to Parliament in January, it was voted down by a historic margin of 230.
The UK is set to leave the EU on 29 March 2019 after voting to leave by nearly 52% to 48% – 17.4m votes to 16.1m – in 2016.
‘No third chance’
Late on Tuesday night, Cabinet Office Minister David Lidington told MPs the documents agreed would “strengthen and improve” both the withdrawal agreement from the EU and the political declaration on the future relationship.
Another document will also be put forward by the government, known as a “unilateral declaration”.
This outlines the UK’s position that there is nothing to prevent it from leaving the backstop arrangement if discussions on a future relationship with the EU break down and there is no prospect of an agreement.
Mr Juncker warned MPs that they would be putting everything at risk if they voted down the deal.
“In politics sometimes you get a second chance,” he said.
“It is what we do with that second chance that counts. There will be no third chance.”
He added: “Let us speak crystal clear about the choice – it is this deal or Brexit might not happen at all.”
Labour leader Jeremy Corbyn urged MPs to vote against the deal when it returns to the Commons, saying the prime minister had “recklessly run down the clock” on negotiations.
Meanwhile, Liberal Democrat leader Sir Vince Cable said Monday’s outcome showed the Brexit negotiations were in disarray.
Independent Group MP Chris Leslie said the government’s “Brexit fudge fools nobody”.
Conservative Dominic Grieve, a former attorney general, said he had looked carefully at the documents overnight and concluded that the changes negotiated did not make “any significant difference” to the backstop.
“It does not allow the UK the right to terminate the backstop at the timing of its own choice,” he told BBC Radio 4’s Today programme.
