Concerns have been raised at the top of government over the legality of contentious Northern Ireland Protocol legislation, which ministers are set to bring forward in the next few days.
Correspondence seen by CSW's sister title PoliticsHome has cast doubt over the government's argument that its plan to override parts of the post-Brexit treaty without an agreement with the European Union would not breach international law.
The Northern Ireland Protocol, agreed by the UK and EU as part of Brexit talks, has been the primary source of tension between London and Brussels since its implementation at the start of last year. It was designed to avoid a contentious hard border on the island of Ireland, but resulted in new barriers to trade between Great Britain and Northern Ireland.
Downing Street argues that it has been left with no choice but to alter the protocol through primary legislation after failing to reach an agreement following many months of negotiations with the EU.
The government insists that this would not break international law. Suella Braverman, the attorney general, approved the plan having concluded that it was legal, The Times reported last month. When unveiling the plan to parliament, foreign secretary Liz Truss said “we are very clear that this is legal in international law and we will be setting out our legal position in due course”.
But in the leaked correspondence, a senior figure advising the government on legal matters says they hold the view that it cannot be "credibly" argued on legal grounds that there is currently no alternative to unilaterally disapplying the treaty, and that it is "very difficult" for the ministers to make that case.
They add that they find that position "more convincing" than the view put forward by Braverman and others that the government was on solid legal footing in pursuing unilateral steps.
The legislation is expected to be published tomorrow or Thursday, although there is some belief that it could be delayed, having not received cabinet sign off as of yesterday morning.
Confirming plans for the legislation last month, Truss said the government had a "clear necessity to act" after the Democratic Unionist Party blocked the formation of a government in Northern Ireland over its opposition to the treaty.
The bill will lay out how the UK will go about disapplying parts of the post-Brexit arrangements for Northern Ireland in order to reduce barriers to trade across the Irish Sea.
The foreign secretary said it would remove "unnecessary bureaucracy" for businesses sending goods from Britain to Northern Ireland. The UK wants to do this by establishing a "green lane" for goods crossing the Irish Sea but staying in Northern Ireland, whereby they will face no checks.
Brussels has urged the UK not to take unilteral action and instead stick with the talks, however.
Maros Sefcovic, the European Commission vice president, last month said the bloc had "serious concerns" about the plans. He warned that the EU would use "all measures at its disposal" in response, further fuelling concerns of a trade war between the UK and its largest trading partner.
There is a feeling among Conservative MPs that Downing Street plans to take a hardline "King Kong approach" to the Northern Ieland Protocol as a means for Boris Johnson to stamp his authority on the party after 148 Tories voted against him in Monday's confidence vote.
Two MPs told PoliticsHome they were preparing themselves for the prospect of having the whip removed if they vote against the legislation when it goes to a House of Commons vote.
One Conservative MP said: "The government's strategy to rebuild trust is a kamikaze one: repeat the law breaking of Owen Paterson and Partygate and force MPs into defending more law breaches. [Tory MPs facing Lib Dems] will be especially delighted."
Tory MP Jesse Norman, the former Treasury minister, in his letter of no confidence to 1922 Committee chair Sir Graham Brady, said Johnson's plan to take unilateral action on the protocol was one of his reasons for pushing for his removal.
He said doing so would be "economically very damaging, politically foolhardy and almost certainly illegal".
Truss last month stressed that the government's preference continued to be reaching a negotiated outcome with the EU, and negotiations are set to continue throughout the summer.
But she told MPs that the post-Brexit treaty did not have the support of Northern Ireland's unionist community, and that the Good Friday peace agreement was "under strain" as a result.
Adam Payne is political editor at CSW's sister title PoliticsHome, where this story first appeared