Brexit: UK could be stuck in 'protracted and repeating' negotiations with EU, government legal advice warns

Attorney general’s assessment published after MPs found government in contempt of parliament

Theresa May’s hopes of getting her Brexit deal through parliament have been dealt a further blow as legal advice given to ministers confirmed the UK could be kept in a customs union with the EU “indefinitely”.

The expert opinion provided by Geoffrey Cox, the attorney general, said the country could end up trapped in “protracted and repeating rounds of negotiations”.

The proposed customs backstop would see new checks on goods travelling between Northern Ireland and Great Britain, Mr Cox said, with the region treating the rest of the UK “as a third country”.

The full legal advice was published after the House of Commons demanded its release and found ministers in contempt of parliament when they refused.

Tory Brexiteers and the DUP immediately claimed the advice showed why Ms May’s Brexit deal should be rejected, while Labour said it highlighted the “central weaknesses” in the prime minister’s plan.

The six-page document drawn up by Mr Cox was released a day after the Commons found that ministers were in contempt by trying to keep it secret. Last month, MPs had voted to order ministers to release the document.

In the guidance, Mr Cox said the UK would not have the right to leave the customs backstop unilaterally, meaning it could “endure indefinitely” until an alternative arrangement is agreed.

The proposed withdrawal agreement “does not provide for a mechanism that is likely to enable the UK lawfully to exit the UK-wide customs union without a subsequent agreement”, he said.

He added: “This remains the case even if parties are still negotiating many years later and even if the parties believe that talks have clearly broken down and there is no prospect of a future relationship agreement.”

Under the proposed backstop, “for regulatory purposes, GB is essentially treated as a third country by NI for goods passing from GB into NI”, he said.

The attorney general also suggested that the EU could seek to ditch the UK-wide customs union element of the backstop and keep only Northern Ireland under EU tariffs and regulations.

That is likely to be seized upon by the DUP, which is opposed to the proposed deal on the grounds that it could see Northern Ireland treated differently to the rest of the UK.

If talks about the future EU-UK relationship break down, Mr Cox said, the EU could submit a request “that the GB elements of the customs union should fall away, leaving only NI in the EU customs territory”.

This would almost certainly be vetoed by the UK and would have to go to arbitration.

Mr Cox warned: “In the absence of a right of termination, there is a legal risk that the United Kingdom might become subject to protracted and repeating rounds of negotiations.”

Commenting on the advice, Sir Keir Starmer, Labour’s shadow Brexit secretary, said: “Having reviewed the attorney general’s legal advice, it’s obvious why this needed to be placed in the public domain.

“All week we have heard from government ministers that releasing this information could harm the national interest. Nothing of the sort.”

He added: “All this advice reveals is the central weaknesses in the government’s deal.

“It is unthinkable that the government tried to keep this information from parliament – and indeed the public – before next week’s vote.”

DUP deputy leader Nigel Dodds said the publication of the advice was “devastating”.

He told Sky News: “We were saying all along that this was the case about an Irish Sea border for customs and single market [regulatory checks]. The attorney general of the United Kingdom has now confirmed that. I think it’s pretty devastating for the prime minister in the sense she’s been trying to deny that.”

He added: “It’s a completely devastating document as far as the prime minister’s plans are concerned.

“The prime minister has taken her government down a road which doesn’t satisfy us and doesn’t satisfy most of our party.”