Protesters outside the Supreme Court erupted into cheers as the UK’s highest court ruled that Boris Johnson’s suspension of Parliament was unlawful.
Chants of “reopen Parliament” and “Johnson out” ripped through the crowds as Lady Hale delivered the judgement.
Labour leader Jeremy Corbyn, former Cabinet minister Amber Rudd and Brexit Party leader Nigel Farage are among the swathes of politicians to react to the ruling, with most calling on Boris Johnson - or his key advisor Dominic Cummings - to resign.
Commons Speaker John Bercow was among the first politicians to respond, saying: “I welcome the Supreme Court’s judgement that the prorogation of Parliament was unlawful."
“The judges have rejected the Government’s claim that closing down Parliament for five weeks was merely standard practice to allow for a new Queen’s Speech," he said immediately after the ruling was announced.
“In reaching their conclusion, they have vindicated the right and duty of Parliament to meet at this crucial time to scrutinise the executive and hold Ministers to account."
Gina Miller, who led the legal challenge against the move to prorogue parliament, described the decision as a win for parliamentary sovereignty.
“Today’s ruling confirms that we are a nation governed by the rule of law. Rules that everyone even the Prime Minister is not above,” she said.
“The ruling today speaks volumes. This Prime Minister must open the doors of Parliament tomorrow," she added.
“MPs must get back and be brave and bold in holding this unscrupulous government to account.”
Meanwhile, rival MPs and former members of Mr Johnson's Cabinet called for the Prime Minister to resign.
Responding from their party conference in Brighton, Labour leader Jeremy Corbyn and Shadow chancellor John McDonnell said Mr Johnson should “consider his position” following the Supreme Court decision.
“The Conservative Party itself should consider their wisdom in electing him as leader,” Mr McDonnell added.
Labour deputy Tom Watson was more direct in his phrasing, tweeting simply: "Boris Johnson should resign."
Liberal Democrat leader Jo Swinson agreed, saying the judges’ decision proved the Tory leader was “not fit to be Prime Minister”.
"The court have found what we all knew all along, Boris Johnson has again proven he is not fit to be Prime Minister," she said.
“This shutdown was an unlawful act designed to stop Parliament doing its job and holding the Government to account."
Liberal Democrat leader Jo Swinson reacts to Supreme Court ruling
She went on: “Given this verdict, Parliament should be sitting so that we can continue to question the Conservative Government on their disastrous Brexit plans.
“This verdict has been unanimously agreed by experienced judges who have considered the case on its merits, acting as impartial guardians of our democratic system.
“The rule of law is an important pillar of our democracy, and those looking to use this opportunity as an excuse to attack these judges would be not only attacking them, but also the entire principle of our legal system.”
Despite personal assurances from the PM, the Cabinet was not shown the legal advice around this prorogation.
This is an astonishing moment and I regret that the PM, who entered office with such goodwill, went down this route. I urge him to work with Parliament to pass a Deal.— Amber Rudd MP (@AmberRuddHR)September 24, 2019
Former Tory MP Amber Rudd, who quit Boris Johnson’s Cabinet earlier this month over the Government’s handling of Brexit, described the Supreme Court’s findings as “astonishing”.
“Despite personal assurances from the PM, the Cabinet was not shown the legal advice around this prorogation,” she tweeted.
“This is an astonishing moment and I regret that the PM, who entered office with such goodwill, went down this route.
“I urge him to work with Parliament to pass a Deal.”
SNP Westminster leader Ian Blackford and Scottish First Minister Nicola Sturgeon both echoed the calls to oust Mr Johnson.
“We must be back in Parliament immediately," Me Blackford said.
“We want to get back to work. On the back of this, Boris Johnson must resign.”
I’m on my way back to Parliament right now from @vicderbyshire @BBCNews - the #SupremeCourt has ruled Parliament was *never* suspended and PM has acted unlawfully - so we should be back ASAP. And #LiarJohnson should turn up and be held accountable for his actions. pic.twitter.com/nbAm2EpAN0— Stephen Doughty MP / AS (@SDoughtyMP)September 24, 2019
Labour MP Stephen Doughty joked that he was already on his way there.
“I’m on my way back to Parliament right now…” he tweeted. “The #SupremeCourt has ruled Parliament was *never* suspended and PM has acted unlawfully – so we should be back ASAP.
“And #LiarJohnson should turn up and be held accountable for his actions.”
The calling of a Queen's Speech and prorogation is the worst political decision ever. Dominic Cummings must go.— Nigel Farage (@Nigel_Farage)September 24, 2019
Brexit Party leader called for Boris Johnson's advisor, rather than the PM himself, to step down.
Describing the suspension of Parliament as "the worst political decision ever", he tweeted: "Dominic Cummings must go."
Supreme Court decision has stopped Johnson in his tracks. Parliament cannot be swept aside by prime ministerial whim. It must resume immediately. This is just the start. Our democracy won’t be safe until we have a written constitution, protecting our rights and rule of law pic.twitter.com/XymfqV8q7n— Caroline Lucas (@CarolineLucas)September 24, 2019
His party's chairman and MEP Richard Tice followed Mr Farage's lead, insiting Mr Cummings should resign "today".
He told the BBC: “What an extraordinary day. The thing now is to focus on what happens next.
“As soon as Parliament is recalled, Boris Johnson is probably going to have to offer his resignation or there may well be a vote of no confidence.”
"Then there is the question of a general election, and really and truly that should be as soon as possible, probably meaning the first half of November.
“And goodness me, what does it say about the so-called master strategist, Dominic Cummings? I trust he’ll be offering his resignation today.”
"We're not leaving the EU on October 31st... when that penny drops, people are going to be increasingly angry"
Brexit Party MEP Richard Tice says Boris Johnson's adviser Dominic Cummings should resign, as Supreme Court rules Parliament suspension unlawful https://t.co/xZ54TdOAam pic.twitter.com/YLlnBXzkzE— BBC Politics (@BBCPolitics)September 24, 2019
Former Green Party leader Caroline Lucas said the Supreme Court’s decision is “just the start”.
“Supreme Court decision has stopped Johnson in his tracks,” she tweeted. “Parliament cannot be swept aside by prime ministerial whim. It must resume immediately.
“This is just the start. Our democracy won’t be safe until we have a written constitution, protecting our rights and rule of law.”
An extraordinary day when parliamentary sovereignty has been upheld
The session is resumed and we need to get back to work - holding to account an Executive that is lurching ever further out of control pic.twitter.com/GbV0UeRjtt— Caroline Lucas (@CarolineLucas)September 24, 2019
She later shared a photo of herself in the Commons holding a sign reading "not silenced.
“An extraordinary day when parliamentary sovereignty has been upheld,” she captioned the image.
“The session is resumed and we need to get back to work – holding to account an Executive that is lurching ever further out of control.”
At least one big relief in the Brexit saga: the rule of law in the UK is alive & kicking. Parliaments should never be silenced in a real democracy.
I never want to hear Boris Johnson or any other Brexiteer say again that the European Union is undemocratic.— Guy Verhofstadt (@guyverhofstadt)September 24, 2019
The European Parliament’s Brexit co-ordinator Guy Verhofstadt hailed the decision as a "big relief".
He tweeted: “At least one big relief in the Brexit saga: the rule of law in the UK is alive & kicking.
“Parliaments should never be silenced in a real democracy.
“I never want to hear Boris Johnson or any other Brexiteer say again that the European Union is undemocratic.”
DUP leader Arlene Foster diverted focus away from the Prime Minister and towards the Government's next steps.
She tweeted: "Our focus must remain: defend the Union, deliver Brexit, restore devolution."