A former British prime minister threatened Wednesday to take Conservative Party leadership candidate Boris Johnson to court if he tries to suspend Parliament to deliver Brexit without a deal.

John Major told the BBC it would be unacceptable and against tradition to shut down Parliament, and he would seek a court ruling to overturn it if it happened. Major’s suggestion is important because Parliament has repeatedly signaled its opposition to a no-deal Brexit, but has no obvious way of stopping it. A legal challenge offers a potential new route.

“You cannot and should not bypass Parliament in this fashion,” Major said. “I cannot imagine how anyone could conceivably think that is right.”

Major’s comments follow a televised debate between Johnson and Jeremy Hunt, the two men seeking to replace Theresa May as Conservative leader and prime minister.

Johnson, who has said leaving the EU by the scheduled date of Oct. 31 is a “do or die” matter, refused to rule out bypassing Parliament to prevent lawmakers from blocking a no-deal departure.

“I’m not going to take anything off the table, any more than I’m going to take no-deal off the table,” Johnson said. “I think it’s absolutely bizarre at this stage in the negotiations for the U.K. — yet again — to be weakening its own position.”

Hunt flatly rejected the idea and suggested it was dangerous.

“When that has happened in the past, when Parliament has been shut down against its will, we actually had a civil war,” Hunt said, referring to the 17th-century showdown between royalists and Parliament over how the country would be governed. Parliament won. King Charles I was tried and executed.

A move to send lawmakers home early would require the formal approval of Queen Elizabeth II. Major said such a request would drag the usually neutral monarch into a constitutional controversy.

“There is no conceivable justification, wherever we are, in closing down Parliament to bypass its sovereignty,” Major said. “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.”

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