Theresa May has been warned she is on course for a “historic constitutional row” unless the government releases its full legal advice on the Brexit deal.
Labour has said it is ready to combine with other opposition parties to start proceedings for contempt of parliament unless the legal opinion of the attorney general, Geoffrey Cox, is published in full.
The DUP, which props up the Conservative government in the Commons, was said to be ready to sign a joint letter with other parties to the speaker, John Bercow, on Monday unless ministers back down.
It potentially represents another hurdle for May as she struggles to win backing for her deal in the crucial commons vote on 11 December.
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It follows a binding Commons vote in November requiring the government to lay before parliament “any legal advice in full” relating to the withdrawal agreement, including that given by the attorney general.
Ministers chose not to oppose the motion – tabled by Labour under an arcane procedure known as the humble address – as they feared a damaging Commons defeat.
The latest row erupted as it was reported that Cox, who is due to make a statement to the Commons on Monday, had warned the UK could be tied to the EU customs union “indefinitely” through the Northern Ireland “backstop”.
The Sunday Times said in a letter sent to cabinet ministers that he advised the only way out of the backstop – designed to prevent the return of a hard border with the Irish Republic – once it was invoked was to sign a new trade deal, a process that could take years.
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“The protocol would endure indefinitely,” he is reported to have written.
The letter was said to be so sensitive that ministers were given numbered copies to read which they were not allowed to take from the room afterwards.
The former Brexit secretary Dominic Raab – who quit last month over the withdrawal agreement – said the legal position was clear.
“The backstop will last indefinitely until it is superseded by the treaty setting out our future relationship, unless the EU allows us to exit,” he told the Sunday Times.
“The EU has a clear veto, even if the future negotiations stretch on for many years, or even if they break down and there is no realistic likelihood of us reaching agreement.
“That’s my view as a former international lawyer, but it is consistent if not identical with all of the formal advice I received.”
Ministers have argued the legal advice is privileged, the same as any advice given by a lawyer to their client, and that government cannot function if it is required to release such confidential material.
However, writing in the Sunday Telegraph, shadow Brexit secretary Sir Keir Starmer said it was essential MPs understood the “full legal implications” before they voted on the agreement. “If the full legal advice is not forthcoming we will have no alternative but to start proceedings for contempt of parliament – and we will work with all parties to take this forward,” he said.
“If ministers stubbornly refuse to obey the order of MPs then they risk triggering a historic constitutional row that puts parliament in direct conflict with the executive.
“Although I accept the longstanding convention that cabinet legal advice should be kept confidential, it’s well established that in exceptional circumstances that convention does not apply. And these are exceptional circumstances.”
Labour sources said that Starmer was ready to sign a joint letter with the DUP’s Westminster leader, Nigel Dodds, the Liberal Democrat Brexit spokesman Tom Brake, and the SNP Europe spokesman Stephen Gethins, asking Bercow to allow a motion “that the government has held parliament in contempt”.
Under Commons rules, if the speaker allows the motion to go before the House and the vote is carried it would then be referred to the committee of privileges which would rule on whether a contempt of parliament had taken place.
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If it were decided that a contempt had occurred, the committee could recommend a suitable punishment which would be put back to MPs to agree.
In theory the most severe penalty is expulsion from the House, although the prospects of that happening would appear remote.
However any finding against the government would be potentially highly damaging for May at a time when politically she is at her most vulnerable.
With the Press Association
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