Boris Johnson's decision to shut down parliament for five weeks has been ruled unlawful by the UK's highest court in a historic ruling. The Supreme Court said the government's advice to the Queen to suspend, or prorogue, parliament was illegal because it "had the effect of frustrating or preventing the ability of parliament" to fulfil its constitutional role. The decision was announced by the court's president Lady Hale, who confirmed it meant the prorogation was "void". House of Commons speaker John Bercow has said parliament will resume from 11.30am on Wednesday. The panel of 11 Supreme Court justices, who sat through a three-day hearing last week on the unprecedented case, gave their unanimously agreed judgment on Tuesday morning in London. The Prime Minister claimed his move to suspend, or prorogue, parliament was to enable his government to produce a new legislative agenda for a Queen's Speech. However, opponents said the prorogation was designed to frustrate parliament and its ability to scrutinise his Brexit policies, and accused Johnson of misleading the Queen when she agreed to suspend parliament. The Prime Minister said he will abide by the court's ruling, even though he does not agree with it. Senior opposition politicians, including Labour leader Jeremy Corbyn and the SNP's Ian Blackford, have called on Johnson to quit Number 10. Announcing the court's decision, Lady Hale made clear the case was "not about when and on what terms the United Kingdom is to leave the European Union. "They are only about whether the advice given by the Prime Minister to Her Majesty the Queen... was lawful." However, the Supreme Court president concluded the shutdown of parliament was "not a normal prorogation". The court's full written judgment can be read here. Lady Hale said: "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." The judge declared the prorogation was "void and of no effect", adding: "Parliament has not been prorogued." She said speakers of the Houses of Commons and Lords "can take immediate steps to enable each house to meet as soon as possible". Lady Hale added that because the prorogation was unlawful, there was "no need" for the court to consider whether the Prime Minister's motive or purpose was unlawful. The judgment reflects a ruling by the Court of Session in Edinburgh that also found the UK Government's conduct unlawful as it had the effect of "stymying parliament". SNP MP Joanna Cherry, one of the key petitioners in the successful Court of Session case, hailed the Supreme Court's judgment as "a huge victory for the rule of law". The SNP's Westminster leader Ian Blackford, meanwhile, urged the Prime Minister to resign. He tweeted: "Supreme Court determines that prorogation was unlawful. Parliament must now reconvene. "We must hold the government to account for its actions. "Boris Johnson should now resign having acted outwith the law. Parliament has not been prorogued. Let's get back to work." Labour leader Jeremy Corbyn also called for the PM to "consider his position" following the Supreme Court's ruling. Addressing Labour conference in Brighton, Corbyn said: "It shows that the Prime Minister has acted wrongly in shutting down Parliament. "It demonstrates contempt for democracy and an abuse of power by him. The Supreme Court, therefore, passes the baton to the speaker to recall parliament. "I will be in touch immediately to demand that parliament is recalled so that we can question that prime minister, demand that he obeys the law that has been passed by parliament and recognise that our parliament is elected by our people to hold our government to account. "A Labour government wants to be held to account. "We wouldn't bypass democracy, and I invite Boris Johnson in the historic words to consider his position." First Minister Nicola Sturgeon meanwhile said the the ruling is one of "truly historic proportions". She earlier tweeted a picture showing her cabinet watching the ruling in the First Minister's residence of Bute House. Speaking in New York, Johnson said the claimants in the English and Scottish cases which led to the Supreme Court hearing want to "frustrate" Brexit. The Prime Minister said: "Obviously this is a verdict that we will respect and we respect the judicial process. "I have to say that I strongly disagree with what the justices have found. I don't think that it's right but we will go ahead and of course parliament will come back." He continued: "I think the most important thing is we get on and deliver Brexit on October 31 and clearly the claimants in this case are determined to frustrate that and to stop that. "I think it would be very unfortunate if parliament made that objective, which the people want, more difficult but we will get on." The PM added: "The prerogative of prorogation is a very old one and it's not, I think, been contested before in this way." Welcoming the ruling, Commons speaker John Bercow told the media on College Green at Westminster that MPs will return to the House on Wednesday morning. He said there would be no Prime Minister's Questions on Wednesday but there would be scope for urgent questions, ministerial statements and emergency debate applications. Buckingham Palace has not yet commented on the ruling. The Queen is still at Balmoral where she is spending her annual summer break.