Boris Johnson's decision to suspend parliament earlier this month was unlawful, the Supreme Court has ruled.

In a historic ruling, the court said the prorogation was "unlawful, void and to no effect" and that MPs and peers should be free to resume sitting immediately.

They dismissed the government's claim that the issue was not a matter for the courts and said the prime minister did not have the right to close parliament if it had the effect of "preventing or frustrating without reasonable justification" the ability of parliament to carry out its functions.

The unanimous ruling by the UK's top judges prompted immediate calls for Mr Johnson to resign.

The court said parliamentary leaders would be free to make arrangements for both houses to resume sitting immediately because, in legal terms, parliament had never been prorogued. Some MPs began to return to the House of Commons within minutes.

Announcing the verdict reached by all 11 judges who heard the case, Supreme Court president Lady Hale said: "The court is bound to conclude that 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.”

The judges dismissed the government's argument that the suspension of parliament was a routine step to allow the preparation of new laws ahead of the Queen’s Speech on 14 October.

Lady Hale said: "This was not a normal prorogation. It prevented parliament from carrying out its constitutional role for five out of the possible eight weeks between the end of the summer recess and exit day on 31 October."

She said the “prolonged suspension of parliamentary democracy took place in quite exceptional circumstances” as Britain prepares to leave the EU, and that "the effect on the fundamentals of our democracy was extreme".

Supreme Court verdict: Boris Johnson prorogation unlawful Show all 16 1 /16 Supreme Court verdict: Boris Johnson prorogation unlawful Supreme Court verdict: Boris Johnson prorogation unlawful The Supreme Court has ruled against Boris Johnson by declaring his government unlawfully shut down parliament for five weeks EPA Supreme Court verdict: Boris Johnson prorogation unlawful Lady Hale handed down the historic verdict, hailed by opposition MPs and anti-Brexit campaigners. She said all 11 judges were unanimous in deciding that the case is “justiciable”, so the government loses that part of the argument. “The court is bound to conclude therefore that the decision to advise Her Majesty to prorogue was unlawful because it had the effect of frustrating or preventing the ability of Parliament to carry out its constitutional functions.” EPA/Supreme Court Supreme Court verdict: Boris Johnson prorogation unlawful Gina Miller and her team react outside the Supreme Court are the verdict. She said: “Today is not a win for any individual or cause. It is a win for Parliamentary sovereignty, the separation of powers and independence of our British courts. Crucially, today’s ruling confirms that we are a nation governed by the rule of law, laws that everyone, even the Prime Minister, are subject to." PA Supreme Court verdict: Boris Johnson prorogation unlawful A person dressed as a caricature of British Prime Minister Boris Johnson in a prison uniform stands outside the Supreme Court AP Supreme Court verdict: Boris Johnson prorogation unlawful Labour leader Jeremy Corbyn called for Mr Johnson to “consider his position” following the landmark decision, while Lib Dem leader Jo Swinson said he was “not fit to be prime minister” Getty Supreme Court verdict: Boris Johnson prorogation unlawful Scottish National Party (SNP) Westminster leader Ian Blackford raises his arms as he comes outside. He said: "This is an absolutely stunning judgement by the Supreme Court today." He went on to say, "we all want to get back to work, and quite frankly, on the back of this, Boris Johnson must resign immediately." AFP/Getty Supreme Court verdict: Boris Johnson prorogation unlawful Crowds outside celebrated the verdict AP Supreme Court verdict: Boris Johnson prorogation unlawful Delegates at the Labour party conference applaud after hearing the news AFP/Getty Supreme Court verdict: Boris Johnson prorogation unlawful Speaker John Bercow said MPs must now “convene without delay” and confirmed the Commons would return at 11.30am on Wednesday AFP/Getty Supreme Court verdict: Boris Johnson prorogation unlawful Gina Miller said: "“As a result of this judgment, Parliament is open, it was never prorogued. I urge MPs to get back to work immediately.” AP Supreme Court verdict: Boris Johnson prorogation unlawful MPs Anna Soubry, Liz Saville Roberts and Caroline Lucas, together with SNP leader Ian Blackford, react. Green MP Caroline Lucas has said the Supreme Court’s decision is “just the start” Reuters Supreme Court verdict: Boris Johnson prorogation unlawful “The UK deserves a Prime Minister and a Government who act with honesty, integrity and in a manner consistent with our constitution, at all times." AFP/Getty Supreme Court verdict: Boris Johnson prorogation unlawful Anti-Brexit supporters react as they gather outside the Supreme Court in London, Tuesday, Sept. 24, 2019 as it makes it's decision on the legality of Prime Minister Boris Johnson's five-week suspension of Parliament. (AP Photo/Frank Augstein) Frank Augstein AP Supreme Court verdict: Boris Johnson prorogation unlawful The SNP’s Joanna Cherry QC says: “Boris Johnson’s position is untenable and he should have the guts to resign.” PA Supreme Court verdict: Boris Johnson prorogation unlawful epa07865617 Protesters react outside the Supreme Court after the result of a hearing on the prorogation of parliament, in London, Britain, 19 September 2019. The Supreme Court ruled that the suspension of parliament by British Prime Minister Boris Johnson was not lawful. EPA/NEIL HALL NEIL HALL EPA Supreme Court verdict: Boris Johnson prorogation unlawful Tom Tugendhat MP returned to the chamber in the House of Commons within minutes of the Supreme Court ruling PA

She added: “Parliament, and in particular the House of Commons as the elected representatives of the people, has a right to a voice in how that change comes about. The effect upon the fundamentals of our democracy was extreme. No justification for taking action with such an extreme effect has been put before the court.”

Lady Hale said it would be for the speakers of the House of Commons and House of Lords to "take immediate steps to enable each House to meet as soon as possible".

Responding to the ruling moments later, House of Commons Speaker John Bercow welcomed the judgement and said he would consult with party leaders urgently.

He said: "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. I

"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. As the embodiment of our parliamentary democracy, the House of Commons must convene without delay. To this end, I will now consult the party leaders as a matter of urgency."

Labour leader Jeremy Corbyn made an immediate statement from the podium at Labour's conference in Brighton, saying Mr Johnson should "consider his position".

He said: "It demonstrates a contempt for democracy and an abuse of power by him. The Supreme Court passes the baton to the Speaker to recall parliament. I will in touch immediately to demand that parliament is recalled so we can question that prime minister, demand that he obeys the law that has been passed by parliament."

"A Labour government would want to be held to account, we wouldn't bypass democracy.

"And I invite Boris Johnson, in the historic words, to consider his position."

SNP MP Joanna Cherry, who led the challenge to prorogation in the Scottish courts, said the ruling was “a huge victory for the rule of law and for democracy” and also called on Mr Johnson to resign.

She said: “There is nothing to stop us members of parliament, such as myself and my colleagues from resuming immediately the important job of scrutinising this minority Tory government as we hurtle towards Brexit.”

Of Mr Johnson, she said: “His position is untenable and he should have the guts for once to do the decent thing and resign."

Supreme Court ruling: Jeremy Corbyn invites Boris Johnson 'to consider his position'

Outside the court, protesters on both sides of the Brexit debate had waited in the rain for the verdict, with demonstrators holding signs reading “defend democracy” and “don’t silence parliament” breaking out in cheers as the news broke.

Mr Johnson had faced heavy criticism for failing to lodge a witness statement detailing his reasoning for the suspension, leaving government lawyers to rely on a 15 August memorandum from a Downing Street legal adviser recommending prorogation to begin from 9 to 12 September.

Judges found that the document did not explain why a five-week prorogation was needed rather than the normal four to six days, the difference between prorogation and recess or consider the impact on achieving an “orderly withdrawal” from the EU.

Government lawyers had argued that Mr Johnson’s advice to the Queen was a “political decision” that could not be ruled on by judges because of the constitutional principle of the separation of powers.

But Lady Hale said courts “have exercised a supervisory jurisdiction over the lawfulness of acts of the government for centuries” and have the power to “decide upon the existence and limits of a prerogative power”.

The Supreme Court found that because the prime minister’s advice to the Queen was unlawful, the prorogation order was effectively a “blank sheet of paper” that had no legal effect on parliament.