Boris Johnson has failed to quash a growing Tory revolt over plans to amend the Brexit divorce deal, as senior figures, including Sajid Javid, joined the rebels.
Mr Javid, the former chancellor, said he would “regretfully” be unable to support legislation that would give the Government the power to go back on parts of the Withdrawal Agreement negotiated by Mr Johnson last year.
He is one of 18 Tory MPs who have publicly opposed legislation which cleared its first Commons hurdle on Monday night, while David Cameron became the fifth former prime minister to express misgivings about it, as seen below.
The rebels include 10 former ministers, five of whom served in the Cabinet. MPs voted to give the UK Internal Market Bill a second reading by 340 to 263 - a Government majority of 77.
They are joined by Lord Hague, who writes in Tuesdays's Telegraph that international law is “not some abstract concept”. Five former Conservative Party leaders have now criticised Mr Johnson’s actions.
Downing Street hinted that the rebels could all have the whip withdrawn if they do not back down, with a source saying “all options are on the table”.
The Prime Minister remained defiant as he opened the debate on the contentious Internal Market Bill, the legislation that would give him the power to override some elements of the Withdrawal Agreement.
He told MPs he needed “the armature of our law” to prevent the EU from imposing barriers to trade across the Irish Sea, saying the Bill “should be welcomed by everyone who cares about the sovereignty and integrity of our United Kingdom”.
Mr Johnson argued that Brussels had made the “absurd and self-defeating” threat of making it illegal for animal products to be sold from Great Britain to Northern Ireland and the EU “still have not taken this revolver off the table”.
MPs have now voted on moving the Bill to its next Parliamentary stage, with the real battle expected next week when rebels are expected to table an amendment demanding the Commons has the final say over whether the Withdrawal Agreement is broken.
Mr Javid, who lost out to Mr Johnson in the Conservative Party leadership contest last year, argued that breaking international law is a “step that should never be taken lightly” and said it was not “clear” why the Government had chosen to do so.
He said: “I will therefore regretfully be unable to support the Bill... and urge the Government to amend it in the coming days.”
Other Tory MPs who have said they will oppose the Bill include Jeremy Wright, the former culture secretary and attorney general; Sir Charles Walker, the deputy chairman of the 1922 committee of backbench Tory MPs, and Rehman Chisti, who resigned his role as Mr Johnson’s freedom of religion envoy to oppose the Government.
In a sign of the growing concern in Downing St, Mr Johnson spoke to several of the rebels by phone, while others received calls from Suella Braverman, the Solicitor General, and Mark Spencer, the Chief Whip, urging them to reconsider and offering them an audience with the Prime Minister.
Lord Hague said: “Whenever I spoke as foreign secretary about the upholding of laws and treaties, to the UN or any errant state, I did so with the utter confidence that my country stood on solid ground. We undermine that ground at our peril.”
The Prime Minister said the measures contained in the Bill to override the Withdrawal Agreement would "never be invoked" if an agreement was reached with Brussels.
He said that if Brussels failed to negotiate in good faith then it would be necessary to introduce the “package of protective powers”.
He said MPs would then be able to vote on whether to rescind the powers, but rebel MPs said they would need to be given a vote before, not after, the powers were used.
Sir Bob Neill, the Conservative MP behind the rebel amendment, said the Prime Minister's promise of a vote did not provide “enough scrutiny for such a constitutionally significant issue”.
The rebels will need to number at least 50 to defeat the Government, as Mr Johnson has an 80-seat majority and the DUP has also said it will vote for the Bill.
Shadow business secretary Ed Miliband said the Prime Minister had “severely damaged” the UK’s reputation as an upholder of the rule of law with his “legislative hooliganism”.
Behind the scenes, Government whips are continuing to try to find a compromise that would satisfy the rebels.
A supporter of the Neill amendment said discussions with the whip’s office had been “perfectly cordial” and insisted discussions to urge the Government to adopt the amendment were ongoing.
They said: “I know that most of us supporters are prepared to work with the Government to ensure terms that both sides are happy with. We do want to support the Prime Minister.”
A separate senior backbencher added: “Many MPs are talking about this as being the Government's Gallipoli. It’s a totally unnecessary battle that we don’t need to have.”
Downing Street’s warning that MPs who rebelled against the legislation could be stripped of the Tory whip was dismissed by rebels as “posturing” and “bluster”.
One said: “It’s one thing when you want an election to expel MPs from the party, it's another when you’re less than one year into your term and face losing your majority.