New fears that UK will breach international law with plan to tear up Northern Ireland protocol

Government legal adviser warns it cannot be argued ‘credibly’ that there is no alternative to unilateral move

New fears have been raised in government that the UK will breach international law if it ploughs ahead with plans to tear up the Northern Ireland Protocol.

In leaked correspondence, a senior legal adviser warned it could not be argued “credibly” that there is no alternative to unilaterally overriding the Brexit agreement.

It would be “very difficult” for the government to make that case, the adviser has told ministers, according to the PoliticsHome website which has seen the correspondence.

Separately, it is believed that James Eadie, the government’s independent barrister on national legal issues, has not been consulted on whether a planned Bill will break international law.

Sky News reported that Sir James has indicated his belief that it will be very hard for the UK to defend its unilateral move as legal – while a former cabinet minister told The Independent it was “unprecedented” not to consult the First Treasury Counsel on such an issue.

Boris Johnson denied in the Commons that Sir James had not been consulted, telling MPs: “Reports this morning are not correct.” His official spokesperson later confirmed that the PM was referring to Eadie, telling reporters it was “not correct to say he hasn’t been consulted in that process”.

However, the spokesperson was unable to say whether Sir James had been asked to give his opinion on the merits of the legal advice which the government chose to accept.

Legislation is expected within days to remove trade border checks in the Irish Sea that Boris Johnson agreed as the price for leaving Northern Ireland within the EU’s single market and customs union territory.

However, it will go much further than border controls – also targeting the role of the European Court of Justice in overseeing disputes and aiming to restore the UK’s ability to decide VAT rates.

Suella Braverman, the attorney general, has concluded the legislation is legal, arguing the greater need is to protect the Good Friday Agreement amid Unionist opposition to the Protocol.

But she has rejected calls to publish her legal opinion. The EU argues the Protocol itself protects the 1998 Agreement by avoiding a hard land border in Ireland.

The legislation is also under threat in the Commons from Tory MPs who oppose it and will now be tempted to use it as a flashpoint to boost the chances of toppling the prime minister.

Jesse Norman, the former Treasury minister who called for Mr Johnson to quit, called it “economically very damaging, politically foolhardy and almost certainly illegal”.

Brussels has threatened a trade war and could even rip up the Brexit trade agreement in retaliation – but is likely to wait until the Bill passes, if it does.

The Bill is expected to introduce a “dual regulatory regime” which would allow goods produced in Great Britain into Northern Ireland and vice versa with no checks.

But, in a move that will fuel doubts about the plan, the government is likely to ask businesses to work out themselves how it can be put into practice.

The EU insists it has put forward proposals to ease the burden of checks and points to the UK’s refusal to sign up to common veterinary rules to reduce the need for much of the bureaucracy

Last month, Mr Johnson admitted he signed up to the trade barriers created by the Northern Ireland Protocol – while saying he hoped the EU would not “apply” them.