UK Prime Minister Boris Johnson's move to prorogue — or temporarily shut down — parliament is unlawful, a court in Scotland has ruled.
Scottish appeal court judges, in a document made public on Wednesday, said the suspension was "motivated by the improper purpose of stymying parliament".
It overturns a ruling by the Court of Session last week that dismissed the case, saying there had been no contravention of the rule of law.
In the ruling that emerged today, judges maintained that Johnson's advice given to the Queen on the reason for suspending parliament for five weeks "was unlawful" and said they would issue an order to declare it "thus null and of no effect".
Lord Brodie, one of the judges involved in the ruling, said: "This was an egregious case of a clear failure to comply with generally accepted standards of behaviour of public authorities."
A spokesperson for the government said it was "disappointed" but planned to appeal the decision with the UK Supreme Court next week.
It added: "The UK Government needs to bring forward a strong domestic legislative agenda. Proroguing parliament is the legal and necessary way of delivering this."
Johnson has been accused of using the suspension scheduled until mid-October as a means to give opposition MPs less time to stop him from pushing through Brexit on the 31st - deal or no deal.
But the prime minister insists he is just following procedure by shutting down parliament in the lead-up to the Queen's Speech, which opens a new parliamentary session by setting out the government's priorities.
Wednesday's ruling has sparked calls from opposition MPs for the parliamentary session to be resumed immediately.
Shadow Brexit Secretary Keir Starmer welcomed the judgement, adding: "no one in their right mind believed Boris Johnson's reason for shutting down parliament.
"I urge the prime minister to immediately recall parliament so we can debate this judgement and decide what happens next."
Meanwhile, Scotland's First Minister Nicola Sturgeon echoed Starmer's request.
She said: "Today’s Court of Session judgment is of huge constitutional significance - but the immediate political implications are clear.
"Court says prorogation was unlawful and null and void - so Parliament must be recalled immediately to allow the essential work of scrutiny to continue."
Downing Street, however, is said to be waiting until the judgement next week after a three-day hearing at the Supreme Court.