LONDON — British Prime Minister Boris Johnson broke the law when he suspended Parliament earlier this month, the country’s top court ruled on Tuesday.

The decision marks a decisive setback for the government, potentially giving lawmakers more time to scrutinize and challenge its Brexit plans.

It’s the latest twist in a saga that has divided and paralyzed the country since it voted to leave the European Union in a June 2016 referendum.

Johnson has vowed to take the U.K. out of the bloc on the current Oct. 31 deadline with or without a deal.

His decision to ask Queen Elizabeth II to suspend Parliament was widely seen as a power grab.

But he suffered a series of defeats before lawmakers were sent home, stripping him of his authority over the issue.

Lawyers for activists and politicians who brought the case argued Johnson had shut down Parliament in a deliberate effort to “silence” them and stop them scrutinizing his policies.

Scotland’s highest court of appeal ruled in their favor, but it was taken up by the Supreme Court as that ruling conflicted with an earlier decision by London’s High Court.

For his part, the prime minister has been adamant his decision to suspend Parliament was legitimate, claiming it was necessary to prepare for a new legislative agenda.

His lawyers indicated last week that he could seek to suspend Parliament again if the court ruled against him.

After uniting the ruling Conservative party around his leadership when he swept to power in July, Johnson has faced growing opposition to his rule.

The suspension, or “proroguing,” was met by protests in the streets of London.

Johnson has also been repeatedly accosted by angry members of the public, and overseen the expulsion of 21 dissenting fellow Conservatives after they supported an opposition plan to try to block a “no-deal” Brexit.

The embattled prime minister, who has seen his own brother quit the government, has been forced to deny that he lied to the queen over his suspension request as he faced growing public pressure over the move.

Johnson says he wants to negotiate a new Brexit deal with Europe but claims he is willing to leave without a deal if necessary.

This is despite the government’s own worst-case-scenario forecast saying it could bring economic pain, civil unrest and shortages of food.

But rebel lawmakers opposed to this “no deal” scenario seized control of the process this month, passing a law that requires Johnson to request a further extension to the U.K.’s divorce date with the E.U.

That leaves him facing the prospect of an embarrassing climbdown from what he termed a “do or die” deadline.

Johnson’s efforts to call an election to solve the impasse were rejected twice.

Under U.K. law a “snap” election can be called if a two-thirds majority of the House of Commons approve it. But opposition parties don’t want to agree to a vote until an extension has been secured.

Johnson maintains that he can negotiate a better deal than that agreed between his predecessor Theresa May and Brussels.

But with just over a month until the deadline it is unclear how much progress he has made.

He is set to hold talks with European leaders this week in New York.

Alexander Smith and Yuliya Talmazan contributed.