Boris Johnson flies back to Westminster facing calls for his resignation and an early election, after a historic Supreme Court ruling plunged his Brexit plans into disarray and his premiership into its deepest crisis yet.

Opposition parties are demanding an immediate statement by the prime minister to the reconvened Commons on the devastating finding of 11 of the UK’s most senior judges that his five-week suspension of parliament was unlawful.

MPs have been put under a strict whip to be in the Commons chamber for the resumption of sittings at 11.30am, 19 days ahead of the 14 October date when Mr Johnson had been planning to allow them back.

Opponents of a no-deal Brexit have vowed to use all parliamentary mechanisms available to ensure the PM complies with a law requiring him to seek an extension to EU withdrawal talks beyond the current deadline of 31 October.

And Labour has made clear it will move immediately after the extension is “locked in” to force a general election which could come within weeks.

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

Downing Street insisted there was no question of Mr Johnson resigning, while the PM himself – who was forced by the court ruling to cut short a visit to the United Nations in New York – vowed to press ahead with plans for a Halloween Brexit and a Queen’s Speech setting out his legislative plans for the year ahead.

Speaker John Bercow has indicated he will be helpful to MPs seeking to put the prime minister’s decisions under forensic scrutiny, making clear he is ready to accept requests for urgent questions to ministers and emergency debates.

And Mr Johnson’s foes made clear that they are not ruling out forcing a vote to find him in contempt of parliament, although this “nuclear option” is not thought to be imminent.

Opposition MPs believe they already have the ammunition they need to trigger a contempt motion, because of Mr Johnson’s earlier failure to publish the full Operation Yellowhammer papers on preparations for a no-deal Brexit and his refusal to release internal communications between aides on the prorogation, as required by parliament.

Members of the so-called “rebel alliance” of MPs across the House are expected initially to focus their fire on Attorney General Geoffrey Cox, who is facing calls for his resignation after a leak showed he advised the PM that the longest prorogation of parliament in modern times was “lawful and within the constitution”.

Mr Cox will face demands for the release in full of the advice on which Mr Johnson based his request to the Queen to shut MPs out of Westminster.

The bid to obtain the secret advice could take the form of a “humble address” to Her Majesty, asking her to require her government to release the document.

And there will be massive pressure on Mr Johnson to dismiss his controversial senior adviser Dominic Cummings, regarded as the driving force behind the PM’s stretching of constitutional and legal conventions in his “do or die” push to get Brexit over the line.

Liberal Democrat Brexit spokesman Tom Brake said the party could also use a series of urgent questions to force ministers to the despatch box to answer questions on issues ranging from the collapse of Thomas Cook to the sale of arms to Saudi Arabia, which MPs have been blocked from scrutinising because of the prorogation.

“We want to demonstrate that parliament is representing the people, as a counter to Boris Johnson’s narrative that it is the people against parliament,” Mr Brake told The Independent.

Supreme Court president Lady Hale delivers the bombshell ruling (Supreme Court/PA)

Aides to Labour leader Jeremy Corbyn confirmed he had been in discussions with leaders of other opposition parties and independent MPs shortly after the court ruling to coordinate moves to ensure no deal is blocked.

“We are determined that there will be an early election,” said a senior Labour spokesman. “The condition is that no deal must be taken off the table first. We will use whatever mechanism is necessary to achieve that.”

Labour is wary of calling a vote of no confidence in the PM until it is absolutely sure that Britain will not crash out of the EU during the election campaign it would trigger. And ministers have not yet ruled out requesting a second prorogation to run down the clock to Brexit day, which the Queen would by convention be expected to grant.

Both Labour and Lib Dems are expected to oppose any Conservative motion for an immediate short recess to allow them to hold the party’s annual conference, due to start in Manchester on Sunday.