It came after the DUP, Labour, SNP, Liberal Democrats, Greens and Plaid Cymru wrote to Mr Bercow demanding the triggering of contempt proceedings. It means Mr Bercow is likely to trigger proceedings which could lead to sanctions against ministers including Mr Cox.

Mr Cox told his critics in the Commons it was time they "grew up and got real" over the legal advice and said: "There is nothing to see here".

However he said he will accept any sanction: "The House has at its disposal the means by which to enforce its will. It can seek to impose a sanction, I fully accept that. I simply say I cannot compromise the public interest."

Mr Cox became the first Attorney General for almost 40 years to answer questions in the Commons about legal advice given to ministers after the Government published a 43-page document setting out its legal position over the EU Withdrawal Agreement.

It fell short of what MPs had demanded when the House of Commons passed a motion calling for the publication of the full legal advice, but it nevertheless contained plenty of controversy.

Mr Cox told MPs: “Let me make no bones about the Northern Ireland protocol. It will subsist, we are indefinitely committed to it if it came into force. There is no point in my trying or the Government trying to disguise that fact.”

His admission represents a significant blow to Theresa May's attempts to win over more than 100 potential Tory rebels ahead of a crunch vote in the Commons next week.

The Speaker is now expected to call a Commons debate and vote on whether the issue should be referred to the Commons authorities.

If the vote is carried the issue is referred to the Committee of Privileges which then rules on whether a contempt of Parliament has taken place.

If it is decided that someone is guilty of contempt, punishments can be recommended which are then put back to MPs to agree.

The toughest punishment which can be handed out is expulsion from the Commons but that has not happened since 1947. Other options include suspension.

On Tuesday the Brexiteer backbencher John Baron will attempt to end the deadlock by tabling an amendment to the vote that would include provision for a unilateral exit from the backstop. He proposes to add a sentence to the motion being voted on next week which says it has been passed “subject to changes being made in the Withdrawal Agreement and in the Ireland/Northern Ireland Protocol so that the UK has the right to terminate the Protocol without having to secure the agreement of the EU”.

Mr Baron discussed the amendment with the Prime Minister, who “listened with interest”, he said.

He told The Telegraph: “I believe this amendment potentially has the ability to end the deadlock because it addresses most people’s concerns on our side and a few people’s concerns on the other side.”

If his amendment is passed, it would be up to Theresa May to wring the further concession out of the EU.