The UK supreme court has ruled that Boris Johnson’s decision to suspend parliament was “unlawful”.

So what does it mean? And what happens next? We’ve lined up some political and constitutional experts to help us explain.

What did the supreme court say?

The supreme court is the highest court in the UK. The 11 judges ruled unanimously that Boris Johnson’s prorogation of parliament was “unlawful”.

Why? Because, in their view, it “had the effect of frustrating or preventing the ability of parliament to carry out its constitutional functions without reasonable justification.” The court says this is an “improper purpose” for prorogation.

The court estimates only a few days would be needed to prepare for a Queen’s Speech, but Mr Johnson wanted to prorogue parliament for five weeks. The judges said: “No justification for taking action with such an extreme effect has been put before the court.”

Is parliament back on?

Because it was unlawful, the government’s instruction to prorogue parliament was “void and of no effect.” In other words, parliament was never prorogued. The judges say it is for the Speakers of the Commons and the Lords to decide what to do next.

Shortly afterwards, Commons Speaker John Bercow announced that he would reconvene parliament tomorrow morning at 11am.

Boris Johnson is to fly back from the UN summit in New York to face MPs. Meanwhile, Jeremy Corbyn — who was due to speak at the Labour conference tomorrow — has moved his speech forward to this afternoon so he can be back in Westminster on Wednesday.

If the prorogation was unlawful, has Boris Johnson committed a crime?

No. And it’s definitely not a prison situation.

Raphael Hogarth of the Institute for Government tells FactCheck: “This was not a criminal offence, but a breach of ‘public law’ — the law which regulated what government can and cannot do.”

Dr Asif Hameed of the University of Southampton explains: “The supreme court ruled that Boris Johnson’s advice to the Queen was unlawful, in that it violated core legal principles of the constitution.”

But, he says, “it’s not the sort of illegality that attracts a punishment such as imprisonment. Many breaches of the law – for instance, defamation or professional negligence — would not attract such punishment. Imprisonment is normally reserved for the criminal law and typically applies to serious criminal offences such as murder or robbery.”

And Professor Michael Gordon of the University of Liverpool points out that in this type of case “courts are assessing whether a public authority [i.e. the government] acted in accordance with the law, rather than whether an individual committed a criminal offence in their private capacity.”

He says this ruling is about whether the original decision was lawful, not whether Boris Johnson should face any personal penalties or legal consequences.

Does Boris Johnson have to resign?

Raphael Hogarth says it’s a political decision whether the prime minister steps down. Dr Hameed agrees, and points out that “there’s no legal duty” on Mr Johnson to do so, and that the supreme court “made no reference to resignation” in its ruling.

He also notes that the court “sidestepped the specific issue about Johnson’s motives in requesting his prorogation,” focusing instead on its effects. Dr Hameed suggests this fact could allow Mr Johnson to “continue to insist that he did not mislead the Queen about his motives, and that the judges did not find against him on this specific issue.”

Dr Marc Geddes of the University of Edinburgh says that “under different circumstances — notably one where we didn’t have such a divided Labour Party nor a looming Brexit deadline — today’s ruling could have spelled the end of Boris Johnson’s career.”

But, in his view, “with Brexit remaining as the main prism through which we see our politicians and political processes, I don’t think that his position will change.”

Does this make an early election more likely?

It’s not in the prime minister’s gift to call a general election, thanks to the Fixed Term Parliaments Act of 2011. That piece of law says two thirds of MPs must vote in favour of a public ballot before it can be held.

Earlier this month, the government tried and failed to get MPs to do just that.

Professor Gordon says: “So now the question is whether those opposition MPs will either vote for an election by a two-thirds majority, which remains unlikely until after an extension to negotiations with the EU has been secured.”

Essentially, a significant chunk of MPs are wary of voting for an election in case Mr Johnson wins and overturns the legislation they passed to try to stop a no-deal Brexit.

Alternatively, opposition MPs could table a vote of confidence to bring down the government. But Professor Gordon says “this seems unlikely” because “while the major defeat the government has suffered in the courts would clearly be a good reason for a vote of confidence, it doesn’t seem to serve the objectives of the opposition at present.”

He continues: “in that sense, an election is only more likely [after today’s supreme court ruling] because parliament will be sitting for longer, and have further opportunities to reconsider whether to take action to bring down the government.”

Dr Geddes goes further, telling FactCheck that he considers the decision “pushes us yet further to the need for a democratic event (a general election or a referendum), which I believe is likely before Christmas.”

What does it mean for Brexit?

Professor Gordon again: “The situation with Brexit is largely unchanged — the Prime Minister is still trying to negotiate a deal with the EU, and will continue with that, although now subject to continuing scrutiny in parliament.”

As for no-deal, Professor Gordon is clear that the legislation created to try to stop it is still binding on the government and is unaffected by the supreme court decision. “The chance of a no deal Brexit remains, if the EU was to refuse to grant a further extension.”

How important is this ruling?

The government is taken to court more often than you might think as part of a process called judicial review.

Perhaps the most high-profile case before today was brought in 2017 by Gina Miller — who was also one of the backers of this week’s battle — and saw the government forced to allow MPs a vote on whether to trigger Article 50.

But the experts we’ve spoken to are unanimous: today’s ruling is massive.

Dr Hameed says: “It’s impossible to overstate how significant this ruling is. Its implications stretch far beyond the current Brexit crisis.”

He predicts the judgement will be read “for years — decades — to come, and not just in the UK.” Other Westminster-style and Commonwealth systems have the power to prorogue, so “the ripple effects of this judgment will be felt in those countries for many years to come as well.”

The IfG’s Raphael Hogarth describes the ruling as “highly significant”. It is not only “a powerful statement of parliament’s role in the constitution” but “also a sign of the supreme court’s own developing role: to police the boundaries of constitutionally proper behaviour.”

Professor Tom Poole of the London School of Economics told FactCheck that today’s decision “rearranges in significant respects some really fundamental aspects of our constitution, especially the relationship between law and politics within it.”

“I can’t think of a bigger UK constitutional law case,” he says.