Brexit news: Hammer blow for May as attorney general says her renegotiated deal can still leave UK in backstop against its will

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Attorney general Geoffrey Cox has said that the UK can still be trapped in the ‘Irish backstop’ so hated by Conservative MPs, despite changes to the Brexit deal won by Theresa May.

The government’s top lawyer did say the prime minister’s efforts had reduced the risk of being trapped in the backstop indefinitely, but in a blow for her hopes of winning a vote on the deal tonight he admitted it could still happen.

It comes as eurosceptic Conservative MPs and Ms May’s DUP allies in government gathered to analyse whether the changes secured by the PM after a late night dash to Strasbourg on Monday, meet their demand that the UK can escape the backstop.

The prime minister must put the new deal before MPs for another critical vote this evening, with another heavy defeat possibly spelling the end of her Brexit strategy and the start of an alternative approach determined by the commons itself.

The backstop is an arrangement in the existing withdrawal agreement that comes into play if the EU and UK fail to agree future trading arrangements by the end of 2020, thus keeping the Irish border open, but also locking the UK into a customs union with the EU on a potentially indefinite basis.

In his official legal advice, Mr Cox wrote that if both sides deploy ”the necessary diligence, flexibility and goodwill” that they are now legally bound to show, it would be “highly unlikely” that the backstop would come into play.

He also said changes set out in three new legal documents laid in parliament on Monday do "provide a substantive and binding reinforcement of the legal rights available to the United Kingdom" if the EU were to try and trap the UK in the backstop, and so “reduce the risk" of that happening.

But he went on: “However, the legal risk remains unchanged that if...because of intractable differences, that situation does arise [where the UK is stuck in the backstop], the United Kingdom would have, at least while the fundamental circumstances remained the same, no internationally lawful means of exiting the protocol’s arrangements, save by agreement.”

The advice will make it harder for Ms May to convince Tories and DUP allies that the UK will never be able to be trapped in the backstop, something they had demanded as the price for their support in tonight’s vote.

Brexiteer Tory MP Andrea Jenkyns tweeted a picture of Mr Cox’s legal advice document and wrote: “The attorney generals advice is that the legal risk remains unchanged.

“Nothing has really changed, and it is still a bad deal so unable to vote for this. We must hold our nerve.”

Shadow Brexit secretary Sir Keir Starmer also quickly responded to the legal advice on the prime minister’s Strasbourg agreement, tweeting a picture with the section that states that the “the legal risk remains unchanged” highlighted in green.

Sir Keir said: “Attorney general confirms that there have been no significant changes to the withdrawal agreement despite the legal documents that were agreed last night.

“The government’s strategy is now in tatters.”

The prime minister reached an 11th-hour agreement with the European Union in Strasbourg late on Monday night and said she “passionately believed” it addressed concerns raised by MPs who feared the backstop would keep the UK in a customs arrangement with the EU indefinitely.

At a joint press conference with European Commission President Jean-Claude Juncker, Ms May said the three new documents agreed provided the legal assurances critics had called for.

They include a “legally binding joint instrument” relating to the Brexit withdrawal agreement, which the government states “reduces the risk that the UK could be deliberately held in the Northern Ireland backstop indefinitely and commits the UK and EU to work to replace the backstop with alternative arrangements by December 2020”.

The second new document is a “unilateral declaration by the UK” which sets out “the sovereign action the UK would take to provide assurance that the backstop would only be applied temporarily”.

The final document is a supplement to the political declaration “setting out commitments by the UK and the EU to expedite the negotiation and bringing into force of their future relationship”.

Ms May needs to win over scores of Tory MPs if she is to have any hope of reversing the 230-vote defeat she suffered when the commons considered her Brexit deal in January.

The DUP, whose 10 MPs prop up Mrs May’s administration, has pledged to carefully analyse the Brexit deal add-ons, though early signals from party insiders are not good for the PM.

If she loses the vote tonight, MPs are set to vote in coming days on whether to take a no-deal Brexit off the table and extend the Article 50 negotiating period.