British Prime Minister Boris Johnson says his government will respect the Supreme Court's ruling that his suspension of parliament is illegal, and is returning early from the UN to attend the parliamentary session.
MPs will return to the House of Commons - where Mr Johnson has no majority - in a sitting tonight. The legislators will be able to hold debates in urgency - as the UK remains without a divorce deal as it prepares to leave the European Union on 31 October.
The prime minister's office says he will fly home a day early from the United Nations to attend the parliamentary session.
Speaking to reporters in New York, Mr Johnson insisted Brexit was going ahead, with or without a deal and he brushed off a reminder that he was legally forbidden from taking the UK out of the EU without parliament's approval.
Labour Party leader Jeremy Corbyn promised to hold Mr Johnson's government to account when parliament returned, again calling for a man he described as "this unelected prime minister" to resign.
"The government will be held to account for what it has done. Boris Johnson has been found to have misled the country. This unelected prime minister should now resign," Mr Corbyn told party members at their annual conference, to thunderous applause and shouts of "Johnson Out!"
"That would make him the shortest-serving British prime minister in history and rightly so," he added. "His is a born-to-rule government of the entitled who believe that the rules they set for everyone else don't apply to them."
A source at the prime minister's office said Mr Johnson would not resign.
A Labour spokesperson said the party would not not support a general election until it was certain Mr Johnson would comply with a law requiring him to seek a delay to Brexit.
Ruling does not prevent a second suspension
Mr Johnson suspended - or prorogued - Parliament for five weeks earlier this month, but Supreme Court judges said it was wrong to stop MPs carrying out duties in the run-up to Brexit on 31 October.
Supreme Court president Lady Hale said "the effect on the fundamentals of democracy was extreme."
During a speech in New York, Mr Johnson said he "refused to be deterred" from getting on with "an exciting and dynamic domestic agenda", and to do that he would need a Queen's Speech.
The court ruling does not prevent him from proroguing again in order to hold one, as long as it does not stop Parliament carrying out its duties "without reasonable justification".
A No 10 source said the Supreme Court had "made a serious mistake in extending its reach to these political matters", and had "made it clear that its reasons [were] connected to the Parliamentary disputes over, and timetable for" Brexit.
But Supreme Court president Lady Hale emphasised in the ruling that the case was "not about when and on what terms" the UK left the EU - it was about the decision to suspend Parliament.
Delivering the justices' conclusions, she said: "The decision to advise Her Majesty to prorogue Parliament was unlawful because it had the effect of frustrating or preventing the ability of Parliament to carry out its constitutional functions without reasonable justification."
Lady Hale said the unanimous decision of the 11 justices meant Parliament had effectively not been prorogued - the decision was null and of no effect.
Lawyers for the government had argued the decision to prorogue was one for Parliament, not the courts.
But the justices disagreed, unanimously deciding it was "justiciable", and there was "no doubt that the courts have jurisdiction to decide upon the existence and limits of a prerogative power".
The court also criticised the length of the suspension, with Lady Hale saying it was "impossible for us to conclude, on the evidence which has been put before us, that there was any reason - let alone a good reason - to advise Her Majesty to prorogue Parliament for five weeks".
Scotland's First Minister, the SNP's Nicola Sturgeon, said the ruling was the most significant constitutional judgement in her lifetime, and it would be "unthinkable" for Mr Johnson to remain in office.
Wales' First Minister, Labour's Mark Drakeford, said the court's decision had been a "victory for the rule of law" and the PM had "tried to play fast and loose with our constitution".
In Northern Ireland, the leader of the DUP, Arlene Foster, said the ruling must be respected, while Sinn Fein's vice president, Michelle O'Neill, said Mr Johnson should resign.
- BBC / Reuters