Boris Johnson is under pressure to reveal the secret sources behind advice given to his government that its controversial plans to tear up the Northern Ireland protocol are legal.
Tory MPs are already braced for the legislation, due to be published on Monday, to breach international law, despite protestations from cabinet ministers that it will be lawful.
Last week, Sir Jonathan Jones, the government’s former top lawyer, said the process of gathering legal advice felt like a “stitch-up” and “like lawyer-shopping”.
Now Labour, the Liberal Democrats and Northern Ireland’s Alliance Party have called on ministers to set aside usual practice and reveal who they consulted.
Shadow Northern Ireland secretary Peter Kyle said the government should release the legal advice it received with “transparency about its origins”.
Lib Dem MP Alistair Carmichael, who served a cabinet minister in the coalition government, said the process of obtaining independent legal advice “should not be tainted by politics”.
“It looks to me like they have gone out looking for a political judgement,” he added. “The rule about not disclosing legal advice depends on the government acting in good faith and getting the best independent advice. It is not apparent that they have done that here, and as a result they should not be allowed to hide behind a rule that they themselves have already broken.”
Sir Jonathan’s criticism followed reports that first Treasury counsel Sir James Eadie, the government’s independent barrister on national legal issues, was not consulted specifically on whether or not the planned bill would break international law.
A former cabinet minister told The Independent that not asking the opinion of the first Treasury counsel was “unprecedented”.
Meanwhile, leaked correspondence showed that a senior legal adviser had warned that it could not be “credibly” argued that there was no alternative to unilaterally overriding the Brexit agreement with Brussels.
Stephen Farry, the deputy leader of the Alliance Party in Northern Ireland, said ministers should be transparent about which lawyers had been consulted.
“In light of the government moving outside the normal process of legal advice, they need to be fully transparent,” he said.
Irish prime minister Micheal Martin has warned that publishing plans to act unilaterally in regard to the protocol would mark a “historic low point”.
Northern Ireland secretary Brandon Lewis said the government intended to set out the “legal basis” for its belief that the legislation would not breach international law.