The legal risk of the UK being tied to EU rules after Brexit “remains unchanged” despite changes to the PM’s deal, the attorney general has said.

Geoffrey Cox said the new agreements reinforced the legal rights available to the UK if post-Brexit trade talks broke down due to “bad faith”.

But the Brexit-backing European Research Group have said they will not be voting for the PM’s deal.

That is a blow to Mrs May’s hopes of getting it through the Commons later.

In a statement, the ERG said: “In the light of our own legal analysis and others we do not recommend accepting the government’s motion today.”

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In his advice, Mr Cox said the extra assurances won by Mrs May in 11th hour talks with the EU “reduce the risk that the United Kingdom could be indefinitely and involuntarily detained” in the backstop if talks on the two sides future relationship broke down due to “bad faith” by the EU.

But he warned that the question of whether a satisfactory post-Brexit deal on a permanent trading relationship can be reached remained “a political judgment”.

And he said “the legal risk remains unchanged” that if no such agreement can be reached due to “intractable differences”, the UK would have “no internationally lawful means” of leaving the backstop without EU agreement.

In a statement to the Commons, Mr Cox later said: “Were such a situation to occur, let me make it clear, the legal risk as I set it out in my letter of November 13 remains unchanged.”

Reaction from MPs

The last time Mrs May’s withdrawal agreement was put to Parliament in January, it was voted down by a margin of 230.

The BBC’s political editor Laura Kuenssberg said it would be a “political miracle of historic proportions” if Mrs May could overturn such a heavy defeat.

Mrs May earlier addressed a meeting of Conservative MPs, in an effort to change the minds of those opposed to her deal.

Conservative MPs leaving the meeting suggested half of those who voted against deal last time will switch to support it later, said BBC’s Chief Political Correspondent Vicky Young.

Former minister Grant Sharps said the vote would be close and Mrs May “needed the DUP” to back her deal.

Work and Pensions Secretary Amber Rudd said she believed the prime minister’s deal would go through “otherwise instability will follow which would be so unwelcome”.

But Mark Francois, a member of the Brexit-backing European Research Group, said he was “wholly unconvinced” by Mrs May’s improved deal.

And ERG chairman Jacob Rees-Mogg said: “The unilateral declaration doesn’t add anything because it simply says ‘we could ask to leave the backstop’.

“We’ve always been able to ask to leave the backstop, that is not in any sense an improvement or a development.”

Labour’s Shadow Brexit Secretary Sir Keir Starmer said: “The government’s strategy is now in tatters.”

What was agreed with the EU?

Documents were agreed after Mrs May flew to the European Parliament with Brexit Secretary Steve Barclay for last-minute talks with Mr Juncker and EU chief Brexit negotiator Michel Barnier.

• 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.
• A joint statement about the UK and EU’s future relationship which commits to replacing the backstop with an alternative by December 2020.
• A “unilateral declaration”. stating there is nothing to stop the UK from leaving the backstop if discussions on a future relationship with the EU break down and there is no prospect of an agreement.

Many MPs fear the backstop, initially agreed by the UK government in December 2017, would keep the country in a customs arrangement with the EU indefinitely.

The PM has claimed the new documents addresses this issue and urged MPs to back the “improved deal”.

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And leading Tory Remainer Dominic Grieve, a former attorney general, said the UK would still not be able to terminate the backstop at a time of its own choosing.

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”.

Read Laura’s blog here.

The EU warns ‘this is it’

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.

Mr Juncker has warned MPs 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.”

The Irish Prime Minister Leo Varadkar said the new agreements showed both sides’ “good faith” – although he made clear they did “not undermine” the principle of the backstop or how it might come into force.

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What could happen this week?

• Theresa May’s deal to face a “meaningful vote” in Parliament later on Tuesday
• If it’s rejected, a further vote has been promised for Wednesday on whether the UK should leave without a deal
• If that no-deal option is rejected, MPs could get a vote on Thursday on whether to request a delay to Brexit from the EU.