Image source, Supreme Court

Thanks for following our live coverage of today's proceedings in the UK Supreme Court.

We'll be back again for more tomorrow.

The hearing resumes at 10:30 BST when we'll be hearing from the lawyer for Prime Minister Boris Johnson, Sir James Eadie.

Then in the afternoon it's Aidan O'Neill, the lawyer for the group led by the SNP's Joanna Cherry.

In the meantime, our news story on the case will continue to be updated with the latest reaction.

Anti-Brexit campaigner Gina Miller, who launched one of the appeals against the five-week suspension of Parliament, left court to cheers and boos from protesters outside.

Demonstrators from both sides of the Brexit debate were standing outside the Supreme Court, just off Parliament Square in central London, during the hearing.

BBC News Channel

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Justiciability is a word that's been used a lot during today's hearing. Essentially it means: can the court answer the question?

"I get the sense that the [Supreme Court] judges consider this case is justiciable so they will decide this question," Stefan Theil, from Oxford University's faculty of law, says.

The English High Court said it could not decide the question of whether the government could prorogue or suspend Parliament.

However, Scotland's highest court later found it could decide that question.

Mr Theil said he believed that, based on Tuesday's proceedings, the UK Supreme Court in London may agree with the Scottish ruling.

The Supreme Court has been hearing two appeals relating to the five-week prorogation of Parliament.

First we heard from Lord Pannick QC, representing Gina Miller, who wants to overturn a High Court ruling which found the suspension of Parliament was lawful.

He argued the issue was a matter for the courts as the "exceptional length" of the prorogation breached the legal principle of parliamentary sovereignty and was an attempt by the prime minister to avoid scrutiny from Parliament.

However, later Lord Keen, representing the government, argued there were examples in history of Parliament being prorogued for political reasons and governments were entitled to do this.

The court resumes again tomorrow when we'll hear from the lawyer for Prime Minister Boris Johnson, Sir James Eadie, and from Aidan O'Neill, the lawyer for the group led by Joanna Cherry MP of the SNP.

The Supreme Court's ruling is expected later this week.

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"This [case] comes back to the foundation of our legal system - the rule of law," Joelle Groger, a law lecturer at Middlesex University, tells the BBC News Channel.

"The second issue is whether or not there are established legal standards against which we can judge this power [to prorogue Parliament]," she says.

"The difficulty, and why it is such an unprecedented case, is that we've never seen this situation where there is not really a piece of legislation," she adds.

Lord Keen, representing the government, has now finished making his submission and the court is adjourned for the day.

Lord Keen ends his submissions by telling the Supreme Court why the government could not prorogue - or suspend - Parliament during the recess for party conferences.

He said that move would involve asking the Speaker of the Commons to recall MPs, something he might only do if it is "in the national interest".

Lord Keen says that once Parliament went into recess, it could not return at will.

He describes this as exposing a "fundamental error" in the arguments of those opposing the government in the Supreme Court.

Image source, UK Supreme Court

Earlier, one of the points put forward by Lord Pannick - the lawyer acting for anti-Brexit campaigner Gina Miller - was about the fact Boris Johnson did not provide a witness statement.

Lord Pannick suggested inferences could be drawn from the lack of a statement from the PM.

But Lord Keen, acting for the government, now reads out part of the opinion from one of the judges in the Scottish case.

"It was not the view of the Inner House that somehow that the absence of an affadavit was of any significance and led to the drawing of any adverse inference whatsoever," he says.

Image source, UK Supreme Court

In court, Lord Keen cites documents which were provided by the prime minister for the Scottish case.

They include a memo from Nikki Da Costa, No 10's former director of legislative affairs.

Lord Wilson, one of the Supreme Court judges, asks whether the documents explain why the government decided to suspend Parliament for five weeks, rather than a shorter period.

Lord Keen replies that it was because the suspension was going to encompass the party conference season in September - when political parties hold their annual conferences.

"Only seven days would be lost", he says.

Lord Keen also points out that before 2002, Parliament did not sit in September as the summer recess continued into October over the conference period.

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Mikolaj Barczentewicz of the centre-right think tank Policy Exchange says Lord Keen, for the government, has so far made two important points.

"First that there is no difference in law as applied by the English court and by the court in Edinburgh - so they are just disagreeing on the application of the same legal standard.

"The second point, which I think is key for the government's case... it is not for the courts to decide on what's a proper purpose for the prime minister to advise the Queen on - whether to prorogue Parliament or not."

Mr Barczentewicz adds: "There is a distinction between what is constitutionally required and what is legally required."

Dominic Casciani
Home Affairs Correspondent

Parliament passed a bill in July,, external requiring regular reports from ministers on progress in rebooting Northern Ireland’s stalled administration.

It was also a legal vehicle to ensure Parliament could sit and hold Boris Johnson’s government to account.

Lord Keen argues MPs had every opportunity to include measures in that bill to prevent a lengthy prorogation - it has the power to define how long Parliament should be closed down - but despite the opportunity in this NI law, it didn't take it.

And therefore, he argues, the courts cannot take for themselves powers to define when and for how long Parliament should be prorogued if Parliament has not taken the power itself to do so.

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Lord Keen says Parliament - if it had wanted to - could have taken action to legislate against being prorogued during a certain time.

He says Parliament had "the opportunity and the means" to determine when it would be prorogued or adjourned.

"If and when Parliament does not wish to be prorogued, Parliament controls that process by primary legislation," he adds.

"The legal limits on the power of the executive are set by Parliament and not by the courts," he tells the judges.

"There are of course a number of examples of where Parliament has exercised the right of control by the use of primary legislation."

Dominic Casciani
Home Affairs Correspondent

One of the key arguments against the PM is that Boris Johnson's prorogation of Parliament for five weeks, for a presumed political purpose of evading scrutiny of his Brexit strategy, is illegal because it's breaches Parliamentary sovereignty.

Lawyers for those challenging the government say that prorogation has to be for a sound and lawful reason - namely in this case the end of a session of Parliament before a Queen's Speech which sets out the government's new agenda.

But Lord Keen, for the prime minister, says there are examples from history of Parliament being prorogued. One from 1948 saw Parliament prorogued for just one day for "naked political reasons", he says.

Without wishing to go into the weeds of that saga, the prorogation came amid a row between the Commons and Lords. One of the Justices, Lady Hale, knows this and says to Lord Keen that closing Parliament on that occasion enforced the will of the democratically-elected MPs.

Lord Keen, for the PM, argues that what the Supreme Court is being asked to do is "go down the road of deciding what is an illegitimate political consideration" to close Parliament. In summary: that's not a legal situation that judges can interfere in.

Lord Keen tells the judges that prorogation has been employed before "where the executive wanted to pursue a political objective - and they are entitled to do so".

Image source, UK Supreme Court

Lord Keen starts to give "clear examples" of where the government has prorogued Parliament for political reasons in the past - and sometimes for an extended period of time than usual.

He mentions the prorogation of Parliament in 1914, at the outbreak of the World War One.

"That clearly was not for the purpose of the King's Speech," he says.

He adds: "Parliament was prorogued for 87 days in 1930 during the onset of the Great Depression."

Lord Keen gives another example of 1948, when Parliament was prorogued to force a bill to be passed.

"This last example was clearly for a party political purpose," he says. "It was a naked political reason."

Dominic Casciani
Home Affairs Correspondent

The Supreme Court has just asked one of the prime minister’s lawyers for clearer written undertaking about how he would abide with a decision against him.

Lord Kerr - one of the longest-serving justices, began interrogating the Advocate General Lord Keen (the PM’s top lawyer in Scotland) about the consequences of losing.

Lord Keen replies: "The consequence could be that he goes to the Queen and seeks the recall of Parliament.”

That doesn’t satisfy Supreme Court justice Lord Kerr who then asks: "Would he prorogue Parliament again?”

Lord Keen, for the PM, replies: "I won't comment on that.”

Lord Carnwath, another of the justices, then says it would be “helpful” to have clearer written undertakings.

Dominic Casciani
Home Affairs Correspondent

In written arguments, Lord Keen, acting for the government, says that the Scottish Supreme Court was wrong because its ruling against the suspension of Parliament amounted to the invention of "a new principle of control over the PM".

Lord Keen adds that applying such a principle "would involve the courts entering the political arena".

The PM’s opponents, Lord Keen adds, have not identified an act of Parliament that Boris Johnson has supposedly broken by closing Parliament for five weeks.

What's more, Lord Keen argues the whole court case is academic because Parliament has already been allowed to sit and debate Brexit.