We apologise to those of you experiencing problems with the sound on the live stream.

We are told it is a problem from within the Supreme Court itself, and is due to the heavy rain in London.

The decision from the Supreme Court is imminent. The judges are due to give their verdict from 10:30 BST.

Dominic Casciani
Home Affairs Correspondent

Image source, Getty Images

The Supreme Court's 11 justices must decide whether the case against the PM's prorogation of Parliament is "justiciable" - which means "can judges theoretically find that he broke some law or other by closing Parliament for five weeks".

The Court of Session in Edinburgh said it was. London's High Court, which is lower, said the opposite.

The justices need to resolve that first question. And if they decide the PM's use of his prerogative, or executive, powers is not justiciable, then it's over. Boris Johnson has won.

If the justices rule that prorogation is justiciable, then they need to rule whether the PM's actions were indeed unlawful. They could rule that he did not break the law. That would mean the PM has won. But the court may say something important about how PM's use the power.

But if the court rules the PM acted unlawfully - that he overreached his powers and deprived Parliament of its sovereignty - then he has lost.

And it becomes a question of "how badly".

Andrew Kerr
Scottish political correspondent

The first thing to look for: is this something the courts can make a ruling on? Secondly, if yes, was it lawful?

The group of politicians who brought the Scottish case, led by Joanna Cherry, have said they’re “cautiously optimistic”.

A senior UK Government source, closely involved with this, said: “We’re stuffed”.

But legal experts have said it’s too close to call.

Legal commentator Joshua Rozenberg has given a brief outline of how the judgement will be handed down just after 10:30 BST.

The oral summary will take a few minutes, he wrote on Twitter, external.

Written copies of the full decision will then be posted online, there has been no advance notice for any of the parties.

"If the court is divided then a simple majority will decide the case. In that event, I would expect Lady Hale to tell us which of the judges are in the majority and which are in the minority. There can be no further appeal," he says.

BBC News Channel

Robert Craig, from the University of Bristol Law School, tells the BBC the consensus among legal watchers is to expect a majority verdict - which will be the Supreme Court's ruling - along with a minority verdict - from the judges who disagree.

"You can never rule out unanimous decisions," he says. But with "lots of strong personalities and opinions" on the court, the expectation is for at least two verdicts.

He says the court will probably have just a single majority verdict, but the minority "can split". In the last case Gina Miller brought to the court, the three minority judges did not give a unified judgement, he says.

Image source, Getty Images

Protesters from both sides of the Brexit debate are beginning to gather outside the Supreme Court.

A man holding a Union Jack umbrella, who gave his name only as Joel, called the Supreme Court case a "stalling" tactic for Brexit.

The Londoner, who said he voted Leave in the EU referendum, said: "It's just stalling Brexit and all the underhand tactics of both sides really is just embarrassing".

Meanwhile, Anne Neville, holding a placard which says "Don't Silence Our MPs", said she would be "disappointed" should Boris Johnson triumph.

The 74-year-old said: "If the Scottish can do it, why can't we? I think the Scots are much more sensible than we are on all sorts of issues."

Image source, PA Media

One of those bringing the legal challenge against the government, campaigner and businesswoman Gina Miller, has arrived at the court.

BBC News Channel

The Supreme Court judges are today being asked to make a historic decision on where the balance of power in the UK constitution lies, a legal expert tells the BBC.

Dr Joelle Grogan, senior lecturer in law at Middlesex University London, says the judges will have to determine the balance of power between Parliament, the Government, the courts and even the monarchy.

“The Supreme Court is going to be making a judgement on all powers, on all fundamental constitutional organs,” she says.

“It’s going to be making a judgement not only on its own role, in terms of deciding the limits of power and of government power, but it’s also going to be making a statement on the place of Parliament and the place of government - and even the place of the Queen, as this does involve advice to the Queen.”

She says it will be “an incredible, incredible judgement in constitutional terms on that principle of the balance of powers, the separation of powers in the UK constitution”.

If the Supreme Court decides Boris Johnson acted unlawfully, things could get complicated.

According to a government document on possible events:

• The court might rule this suspension unlawful, but their reasons might leave open the possibility of proroguing Parliament for the same time period in a different, lawful way;
• The judges could decide that the only lawful option is for the prime minister to recall Parliament before 14 October. Lawyers for Mr Johnson said he would comply, but it would require "extensive arrangements" to draw up a new Queen's Speech and get ready for the ceremonial State Opening of Parliament;
• The judges could declare the suspension unlawful, meaning Parliament would remain in session as if it had never stopped. The government said it might still be able to consider suspending it again.

BBC Radio 4

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Former foreign secretary Jeremy Hunt told BBC Radio 4's Today programme prime ministers take decision with politics in mind.

He said: “No-one should be particularly surprised if prime ministers take decisions with political considerations in mind.

“I think prime ministers take every decision with political considerations in mind and in the end the substantive issue here is would Parliament have time to pass a law taking no-deal off the table?

“And they did have time to do that, so I think we will see what the judgement is.”

Clive Coleman
BBC legal correspondent

The Supreme Court has to resolve two dramatically contradictory rulings.

First off, it will have to decide if prorogation is a matter for the courts and whether there are meaningful legal standards against which it can be judged.

If it decides that it is not a matter for the courts, Boris Johnson wins and some will see that as a victory for common sense, some will see it as a failure of the courts in their constitutional duty to act as a check on the abuse of executive power.

If the Supreme Court decides that it is a matter for them, then it could rule that Boris Johnson’s advice to the Queen was lawful, meaning Boris Johnson wins and generating the same reaction.

Or it could rule that his advice to the Queen was unlawful, either because of his improper motivation to stymie or frustrate Parliament – that is what the Scottish court found – or perhaps more likely that the effect was that legislation was lost and Parliamentary scrutiny was improperly denied.

The effect of that would be that Boris Johnson loses – both are bad for him but a ruling that he misled the Queen through an improper motive would be especially bad and there would be calls for his resignation in that scenario.

The court could also put more pressure on the government by ruling that the order to prorogue Parliament is quashed – meaning MPs could in effect just walk back into Parliament. But the court cannot say Parliament must reconvene or when it can reconvene.

Speaking in New York, Boris Johnson said his government "fully respects the law".

"I am going to wait and see what the judgement is but I want to stress that this is a government that fully respects the law and fully respects the judiciary," he said.

"But we also think that it is sensible for parliament to have its say, absolutely, and that is why there is ample time before the end of October for them to do just that."

Boris Johnson will be in New York when the judgement is announced. But what has he said so far?

In his latest statement, the prime minister refused to rule out suspending Parliament for a second time, should he lose.

Parliament is currently due to return on 14 October, with the UK scheduled to leave the EU on 31 October.

Plenty of time, the PM says, for MPs to consider Brexit before it happens. Critics say the prorogation is unusually long at a critical time for the country.

Image source, PA Media

The battle in the Supreme Court over the shutdown of Parliament is a historic test of the powers of the prime minister, MPs and the courts.

Despite crowds of people on both sides of the Brexit debate protesting outside, the court was keen to emphasise that the case is not actually about Britain leaving the EU.

Instead, Lady Hale, president of the Supreme Court, said it is "solely concerned" with whether it was lawful for Boris Johnson to suspend Parliament through a process called prorogation.

Read more here.

The judgement is due at 10:30 BST.

Supreme Court President Lady Hale, the court’s most senior judge, will lead proceedings.