LONDON — A Scottish court ruled on Wednesday that Prime Minister Boris Johnson’s decision to suspend Parliament was unlawful, a remarkable rebuke of the government’s hard-line tactics in trying to pull Britain out of the European Union.
A panel of three judges in the Court of Sessionfound that the decision to send lawmakers home for five weeks at the height of the Brexit crisis was “unlawful because it had the purpose of stymying Parliament.”
In so doing they reversed a decision last week not to intervene in the case. Britain’s Supreme Court had already said it would hear an appeal in the case next week, and the British government has said it will file an appeal as well.
The ruling said that the court would make an order declaring that the prime minister’s advice to Queen Elizabeth II asking her to suspend Parliament, and the suspension of Parliament itself, was unlawful “and is thus null and of no effect.”
The group of lawmakers who brought the case called for Parliament to be immediately reconvened, but that remained in doubt.
Mr. Johnson, who is committed to pulling Britain out of the European Union by Oct. 31, with or without a deal governing future relations, decided to send Parliament home as lawmakers began making clear that they would try to block his path to an abrupt Brexit.
While it is within a prime minister’s rights to suspend Parliament, those suspensions usually last for only a few days. Scholars called it constitutionally suspect, if not downright unconstitutional, though many doubted that the courts would intervene.
The suspension began on Tuesday, and it was scheduled to prevent Parliament from sitting until mid-October, only weeks before Britain could crash out of the European Union without a deal.
Lawmakers moved quickly enough before the suspension that they passed a law seeking to force Mr. Johnson to ask for a Brexit delay if he did not have a deal in place by late October, though Mr. Johnson has vowed that he would never ask for an extension.