Philip Hammond has set himself on a collision course with Boris Johnson as he announced he would back legal action against the leadership frontrunner if he tried to suspend Parliament.
The Chancellor said there would “certainly” be a move to resort to the courts if the next Prime Minister tried to push through no deal by “proroguing”Parliament.
Mr Hammond said he “strongly supports” Sir John Major’s proposal to seek a judicial review.
Mr Johnson has repeatedly refused to rule out suspending Parliament if he becomes Prime Minister, arguing it would weaken the UK's negotiating position to take any option off the table. His rival Jeremy Hunt has ruled it out.
Mr Hammond told Bloomberg: ““If anybody were to attempt to shut down Parliament in order to carry out a course of action which Parliament is known to oppose, that would be very serious indeed,” Hammond told Bloomberg TV.
“That would provoke a constitutional crisis, and if we aren’t able to prevent that course of action through Parliament then certainly there will be resort to the courts,” Mr Hammond said. “I strongly support the position that Sir John Major has taken”.
David Lidington, Theresa May's de facto deputy, said it would be a "constitutional outrage" for any government to prorogue Parliament to "stop it debating a subject which the government of the day found uncomfortable".
"I think that the precedent that that would set, for perhaps a hard-left government of the future, would be very damaging indeed," he told BBC's Good Morning Scotland.
"So I suspect whichever candidate wins as prime minister will fight shy of that, I would certainly do whatever I could to avoid such an outcome."
Sir John said on Wednesday suspending Parliament would risk dragging the Queen into the toxic political row over Brexit.
“There is no conceivable justification, wherever we are, in closing down Parliament to bypass its sovereignty,” the former prime minister told BBC Radio 4's Today programme.
“I seem to recall that the Brexiteers, led by Mr Johnson, actually campaigned in the referendum for the sovereignty of Parliament. They can't be concerned for the sovereignty of Parliament except when it is inconvenient to Mr Johnson.”
Mr Johnson described Sir John's intervention as “very odd”.
Any request to prorogue Parliament has to be approved by the Queen. Sir John said it was almost inconceivable she would refuse a request from a prime minister, but it would put her “in the midst of a constitutional controversy that no serious politician should put the Queen in.”
Decisions made by a monarch cannot be challenged in court, so Sir John said he would seek a High Court ruling on the legality of any advice given to her by the Prime Minister.
“I for one would be prepared to go and seek judicial review to prevent Parliament being bypassed,” Sir John, who is supporting Foreign Secretary Mr Hunt in the leadership race, said.
It comes as Greg Clark warned “many thousands” of jobs will be lost across the UK in the event of a no deal Brexit.
The Business Secretary told Sky News in an exclusive interview he was certain jobs would go in no-deal as he implored colleagues to "strain every sinew to avoid that".
Asked how many jobs could be lost, he replied: "It's many thousands of jobs. Everyone knows that".