Sir John Major today announced he is prepared to fight Boris Johnson in the High Court to stop him forcing through a No Deal Brexit .
The former Tory Prime Minister confirmed he would seek an "immediate" judicial review if Parliament is suspended to before the October 31 deadline.
He also sensationally accused his own Conservative Party of putting party interests before the country over the issue.
The extraordinary intervention comes after Mr Johnson - the frontrunner to become PM on July 24 - refused to rule out "proroguing" Parliament before the Brexit deadline.
Such a move would block MPs from voting to prevent No Deal.
Sir John said prorogation would drag the Queen into a constitutional sticky situation.
And he told BBC Radio 4's Today programme: "I think this is completely and utterly against Parliamentary tradition and against the way the government should work.
"If that were to happen, I think there would be a queue of people who would seek judicial review.
"The Queen's decision cannot be challenged in law.
"But the Prime Minister's advice to the Queen can, I believe, be challenged in law.
"And I for one would be prepared to go and seek judicial review to prevent Parliament being bypassed."
He added: "The Prime Minister would be bypassing Parliament. That is simply not acceptable."
And he said: "It is a very easy thing to say no to - 'no, I am not going to try and bypass Parliament' - but Mr Johnson has failed to do so."
MPs launched a bid this week to stop Parliament being prorogued
Last night Dominic Grieve, the Tory MP behind the bid, said peers could revive the attempt in the House of Lords.
Quizzed on Sir John's comments, BoJo backer Matt Hancock today insisted "I don't foresee" a prorogation happening.
But Boris Johnson himself refused to rule out proroguing Parliament when he was quizzed in an ITV debate with Jeremy Hunt last night.
He said: "I'm not going to take anything off the table.
"I think it would be absolutely bizarre at this stage in the negotiations for the UK, yet again, to be weakening its own position."
Mr Johnson has promised to take the UK out of the EU on Halloween "do or die" after the date was repeatedly delayed.
But Remainer Sir John told the BBC: "Rushing to an artificial date on October 31 could be disastrous if people are not ready."
He added: "It will be difficult in any event.
"But this date of October 31 has a great deal more to do with the election for leader of the Conservative Party than it has with the interests of the country.
"And that is the wrong way round.
"The interests of the country must come first, before the interests of the Conservative Party and before the interests of any candidate in that election."
