Pressure on the government to provide details of legal advice about a possible Brexit deal is growing, with the DUP, Labour and Lib Dems demanding it be published, following calls from cabinet ministers to see the full document.
One option could be for Labour to seek to force publication via a Commons motion, as the party did with the government’s Brexit impact assessments.
Jeffrey Donaldson, the DUP’s chief whip at Westminster, said the party, which supports Theresa May in government, would like to see the full document published, allowing not only ministers but MPs and the public to assess it.
The shadow Brexit secretary, Keir Starmer, said the advice must be released to MPs so they can scrutinise the document, while the Lib Dems called for the advice to be published in full.
The advice, drawn up by the attorney general, Geoffrey Cox, at the request of Theresa May, looks into the various options connected to the backstop, seen as the final major impasse before a deal can be agreed.
At a cabinet meeting on Tuesday, Cox gave ministers a summary of the advice, and told them that if the UK insisted on the right to unilaterally end a backstop, opposed by the EU, it increased the risk of no deal.
It is understood that some ministers, among them Michael Gove, asked the prime minister whether they could see the full legal advice drawn up by Cox, rather than just hearing his summary and interpretations.
Donaldson told BBC Radio 4’s Today programme: “It’s in the public interest that we understand fully what is happening here. We’ve had that commitment already from the government, that they will tell us what the legal advice they have is in relation to the backstop.”
He said: “If the House of Commons is going to have a meaningful vote on a deal upon which this legal advice is very important, then I think people are entitled to know what that legal advice is.”
The Lib Dems called for the advice to be published. The party’s Brexit spokesman, Tom Brake, said: “Refusing to publish legal advice on Brexit makes a mockery of the discredited mantra ‘take back control’.”
Speaking in Brussels, where he is meeting EU leaders, Starmer said a backstop agreement had to be robust, meaning it was “essential MPs are given the opportunity to scrutinise the attorney general’s legal advice before voting on the final deal”.
He said: “The public have the right to know precisely what the cabinet has signed up to and what the implications are for the future.”
Labour’s aim would be for the advice to be available to MPs, as happened with the Brexit impact assessments. There were made available after Labour forced their release through a so-called humble address motion.
This, or an amendment to a bill, remain options for extracting the legal advice, but it is understood Labour want to first await the government’s response.