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”.
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 on Monday evening, 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.
Monday morning government blues have been replaced by Tuesday morning nervous hopes.
The government does not suddenly expect its Brexit deal to be ushered through at speed, cheered on by well-wishers.
It does, however, believe that Monday night’s double act in Strasbourg by Theresa May and Jean Claude Juncker puts it, to quote one cabinet minister, “back in the races”.
The extra assurances wrought from weeks of talks with the EU will move some of the prime minister’s objectors from the “no” column to the “yes”.
What was agreed on Monday?
Mrs May flew to the European Parliament late on Monday with Brexit Secretary Steve Barclay for last-minute talks.
In discussions with Mr Juncker and EU chief Brexit negotiator Michel Barnier, two documents were agreed by all parties.
Cabinet Office Minister David Lidington then told MPs the documents would “strengthen and improve” both the withdrawal agreement from the EU and the political declaration on the future relationship.
Mrs May said it could be used to start a “formal dispute” against the EU if it tried to keep the UK tied into the backstop indefinitely.
The EU has said the backstop would apply temporarily.
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.