- Video report by ITV News Political Correspondent Carl Dinnen
Cross-party MPs have staged a protest in Parliament after it was ruled Boris Johnson's decision to prorogue was "unlawful" and "improper".
The three senior judges who made the ruling at Scotland's highest civil court said the suspension of Parliament was therefore "null and of no effect".
A group of MPs who previously signed the Church House Declaration - a plan to sit elsewhere should Parliament be shut down - gathered outside the Palace of Westminster to show their support for the court ruling.
After telling reporters outside Parliament they would find ways to hold the government to account, the group, which included Lib Dem leader Jo Swinson, returned to the Commons chamber to continue the protest.
The government said it is "disappointed" by the court ruling and will appeal the ruling at the Supreme Court, adding proroguing Parliament was "legal and necessary".
No formal order will come before Tuesday, when the Supreme Court will hear the case.
The ruling comes a day after the prorogation took place in the early hours of Tuesday, with Parliament now suspended for five weeks.
From outside Parliament, Liberal Democrat leader Jo Swinson told ITV News: "(The government) cannot evade scrutiny, we are already working cross-party, we have done that effectively to plan our next steps."
She added: "The display that we've had today shows how willing people are to do that, so this won't be the last that you hear from how MPs are going to hold the prime minister to account."
Once inside the Commons chamber, protesting Labour MP Jonathan Reynolds tweeted an image of himself on the green benches, adding: "Reporting for duty."
Earlier, party colleague Luke Pollard also shared a picture of himself in the Lobby, adding: "Quietly and peacefully I have gone back to sit in my usual spot in the House of Commons.
"No shouting or scuffles - just a quiet statement about our democracy. Boris Johnson's prorogation of Parliament is unlawful. MPs should be here debating the national crisis. #recallparliament"
The legal bid to challenge the suspension of Parliament by a cross-party group of 70 parliamentarians was initially rejected at the Court of Session, but the appeal was successful.
A summary of the court opinion, published by the Scottish Courts and Tribunals Service, said Mr Johnson's decision to prorogue Parliament was "motivated by the improper purpose of stymying Parliament".
It went on: "The Court will accordingly make an Order declaring that the Prime Minister's advice to HM the Queen and the prorogation which followed thereon was unlawful and is thus null and of no effect."
Labour leader Jeremy Corbyn said it was "a landmark ruling" when a court rules "it is unlawful to prorogue Parliament".
He added: "These are interesting times, when courts rule in favour of democracy, against a Prime Minister who wants to shut down our democracy."
On the supreme court ruling he said "whatever happens next week, we will continue to press for parliament to be recalled".
At the appeal hearing on Friday David Johnston QC, representing the UK government, had argued it was not for the courts to get involved in what was a political decision.
Nigel Farage, leader of the Brexit Party, told ITV News that he "simply can't believe" the decision.
He said: "This is absolutely ridiculous. How can it be unlawful to present a Queen's Speech?
"It's a new prime minister, it's a new cabinet, we've had one of the longest-running sessions of parliament in centuries, how can it be unlawful for the Queen to go into Parliament next month to lay out the government's programme - including its policy on Brexit?" he said.
His comments came as he again offered Boris Johnson the chance of an election "non-aggression pact" where the Brexit Party would not field candidates in seats where the Tories had the best chance of defeating Labour or the Lib Dems."
"Between us, Boris would win a big parliamentary majority. Between us, we'd be unstoppable," he added.
However, Number 10 said the Prime Minister would not do a deal with the Brexit Party leader.
A senior Conservative source described Mr Farage and Brexit-campaigning ally Aaron Banks as not being "fit and proper", and said they should never be "allowed anywhere near" government.
Labour's shadow attorney general Shami Chakrabarti said the ruling shows that Prime Minister Johnson "is not above the law".
She added: "Labour will not allow his elitist shutdown of Parliament to enable him to dodge scrutiny and force through a disastrous no-deal Brexit."
Judge Lord Doherty, who originally dismissed a challenge against the suspension at the Court of Session last Wednesday, said it is for politicians and not the courts to decide.
But three judges of the Inner House, the supreme civil court in Scotland, disagreed with Lord Doherty's ruling.