Ministers have released a summary of the Brexit legal advice, which spells out that the Northern Ireland backstop will continue indefinitely “unless and until” the UK and the EU are able to agree alternative customs arrangements.

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The document, which falls short of the full legal advice demanded by the Commons last month, is likely to provoke a row in parliament. Cabinet sources have repeatedly said that the full legal advice contains stark warnings about the backstop that are not included in the summary.

Over the weekend it emerged that Geoffrey Cox, the attorney general, had written to cabinet ministers warning: “The [backstop] protocol would endure indefinitely.” On Monday afternoon he will give a statement to MPs and take questions about the controversial backstop and whether the UK can get out of it easily.

The summary document says that the backstop will continue to apply “unless and until its provisions are superseded by a subsequent agreement between the UK and the EU establishing alternative arrangements”.

Alternative arrangements are intended to be either a new EU-UK free trade deal, which is expected to take years to negotiate, or new technologies to avoid a hard border returning in Ireland, which are also expected to take years to develop.

The document also makes clear that the backstop is one of the few areas of entire Withdrawal Agreement, the legal treaty governing the UK’s exit from the EU, that does have a potential expiry date.

The entire treaty, meanwhile, “does not contain any provision on its termination,” the official document says, meaning that “it is not possible under international law for a party to withdraw from the Agreement unilaterally.”

Labour and the DUP have both threatened to complain to the Speaker of the Commons that ministers are in contempt of parliament for failing to release the full legal advice, after the government was defeated in a vote on 13 November, where MPs successfully demanded to see the whole legal advice.

Labour is expected to push for the government to be found in contempt of parliament if that is not published by Monday night. A Labour source said “This document falls far short of what parliament demanded. It is not the full legal advice.



“We will wait to hear the attorney general’s statement in the Commons this afternoon and then decide how we intend to proceed. However, ministers should be aware that they are treading on very thin advice indeed.”

Hard Brexiters and the DUP have both complained that the backstop would bring Northern Ireland into closer regulatory alignment with the EU than the rest of the UK – and fear that Brussels could trap the UK in it permanently.

Exiting the backstop would be by mutual agreement between the UK and the EU, via a joint committee made up of equal number of representatives of both sides. If the committee cannot agree, the matter would be referred to a five-strong arbitration panel with five members, two from each side and an independent member.

That panel would consider if either sides had acted “in good faith” in refusing to agree an end to the backstop – but adds that it would be difficult to prove the contrary. “A tribunal would only find a breach of the duty of good faith if there was a clear basis for doing so,” the legal summary adds.