Boris Johnson is set to open up another rift within his party, as his own MPs warn that controversial plans to override the Northern Ireland protocol go against key Conservative principles.
Tory MPs are already braced for the bill to breach international law, despite ministers’ protestations to the contrary.
A leaked briefing paper being shared among Conservative MPs describes the move, which experts have warned could provoke a trade war with the European Union, as “damaging to everything the UK and Conservatives stand for”.
The move could be as devastating to the reputation of the party as the Iraq war was for Labour, it adds.
Fears that the legislation will be used by Mr Johnson to stage a “show of strength” against Brussels were fuelled when a cabinet minister said EU countries were being “disingenuous” in their attitude to the protocol, which was jointly agreed by the UK and the EU as part of Mr Johnson’s Brexit deal.
Labour’s Jenny Chapman accused the government of deliberately “making Brexit worse” in order to divert attention from the embattled prime minister, just days after four in 10 of his own MPs voted to oust him from Downing Street.
The latest row erupted as one senior Tory MP, Charles Walker, said he would not contest the next general election because of the “guerrilla warfare” within the party.
Legislation designed to override parts of the protocol will be published on Monday.
Opposition parties have demanded that ministers reveal the source of legal advice suggesting that the government’s plans would not breach international law, following allegations it had gone “lawyer shopping”.
Many Tory MPs see the rabble-rousing over Brexit as a lurch to the right designed to shore up support for the prime minister after last Monday’s damaging confidence vote.
But the decision to push ahead with the protocol legislation risks alienating more moderate MPs, especially in Lib Dem-facing seats in the south of England.
Voters in these areas are seen as less likely to care about Brexit, and more likely to be upset by the sight of the government breaching its international obligations.
The briefing paper, the contents of which were first reported by the Politics Home website, also warned that the legislation risked alienating the swing voters needed to protect the union.
Rebel Tory MPs believe Mr Johnson is on borrowed time in Downing Street. They hope to spend the next few weeks persuading the 32 MPs they are hoping will switch sides that the Tory leader is a busted flush.
Before last week’s confidence vote, government sources made clear that the prime minister wanted to calm the rhetoric around Brexit, and criticised explosive briefings from allies of the foreign secretary Liz Truss.
It is unclear whether or not the legislation will also have one of its desired effects – convincing Northern Ireland’s DUP to re-enter power sharing.
Government sources said they were hopeful that the party would set out some possible next steps once it saw the detail of the bill, but would not be drawn further.
Irish prime minister Micheal Martin has already warned that the publication of a bill enabling unilateral action on the Northern Ireland protocol would mark a “historic low point”.
Labour, the Liberal Democrats and Northern Ireland’s Alliance Party have demanded ministers reveal who they consulted for legal advice on the bill.
Shadow Northern Ireland secretary Peter Kyle said ministers should release the maximum possible legal advice with “transparency about its origins”.
Lib Dem MP Alistair Carmichael, who served as a cabinet minister in the coalition government, said: “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.”
Stephen Farry, the deputy leader of the Alliance Party, said ministers should be transparent about which lawyers were consulted.
“In light of the government moving outside the normal process of legal advice, they need to be fully transparent,” he said.