The prime minister says the suspension of parliament is to allow the government to set out a new legislative agenda in a Queen's Speech when MPs return to parliament on 14 October.

But those challenging his decision argue that it is designed to prevent parliamentary scrutiny of the UK's impending exit from the EU on 31 October.

So what will the Supreme Court decide?

Asked by another journalist how I thought things would all pan-out, I looked at the two opposing groups of protesters outside the court.

One, holding banners stating that the prime minister lied to the Queen, believes that by proroguing parliament Boris Johnson is engaging in a power grab that will stifle democracy.


The other group 10 metres away, standing behind "Leave Means Leave" banners, believe that MPs are the villains of this piece and the whole case is merely an attempt to undermine what they voted for in the EU referendum.

So, I wondered what I would do as a Supreme Court justice to cut a middle-ground between the two? What is the path of least resistance?

Image: Remain and Leave protesters gathered outside the Supreme Court

My initial thought was that as parliament has proven it can defend itself on this matter, by passing legislation to force the PM to extend the Brexit deadline if he doesn't get a deal, the court might decide it should not intervene in this instance.

In other words, the PM's spectacular defeat in the Commons actually strengthens his case in court.

There's a problem with this assumption. Firstly, the Supreme Court only concerns itself with the law, not with what will best bring together two divided groups of protesters.

Secondly, this case could set a precedent for how governments behave in the future - it's not just about the here and now.

Even if the Supreme Court agreed with my logic, they would have to consider whether their decision closes the door on legal intervention in the future if, for example, it is ever the case that a prime minister is successful in their attempt to totally disable parliament.

As it stands, there have been two opposing judgments.

Brexit oppponent hopeful of court win

Last Wednesday, Scotland's highest court said the suspension was unlawful and an "egregious" attempt to stymie parliament.

However, a week earlier the High Court of England and Wales rejected a similar case, saying the matter was political and not something judges should interfere in.

All 11 judges on the Supreme Court will now decide on a crucial question: how far Britain's unwritten constitution limits the power of the prime minister and whether Johnson's advice to the Queen was therefore illegal.

I put my hypothesis to Joanna Cherry, who'd brought the successful case against the government last week in the Scottish courts, that essentially parliament has proven it didn't need the Supreme Court - the case was nulled by their success.

Sky News interview used as evidence

Her response: "It's not that we don't need the courts. I think the way to understand this is... Lord Drummond Young, one of the three Scottish judges said 'it is not the job of the courts to politically scrutinise the government - that's the job of parliament'.

"But if parliament has been suspended and prevented from doing its job of scrutinising government then courts can step in, if it's being done for unlawful purpose and they found it had been done deliberately to prevent parliamentary scrutiny."

This is about whether the executive is trying to override that parliamentary power.

But the circumstance of this prorogation is also a factor. The looming Brexit deadline is an essential part of the case.

Indeed, there was a moment in the Supreme Court where some of the 11 justices began to ask what other (non-Brexit) parliamentary business might be affected in the five weeks that parliament has been prorogued.

Lord Pannick, making the legal case against the government, didn't know. And it was clear that to him, it didn't matter.

His legal argument rests on the question of whether Mr Johnson was making proper use of his right to suspend parliament, or was he using it to avoid parliament's rightful duty to scrutinise his actions in these crucial weeks leading to the UK's departure from the EU.

In response to this, Lord Richard Keen QC, the advocate general for Scotland, representing the UK government, argued that parliament "maybe prorogued for a variety of reasons, political, as much as formal".

He said this point had been accepted by the divisional court in its judgment and added: "Indeed, the divisional court went on to observe that even if one was looking only at the matter of the provision of a new Queen's Speech, it was not for the courts to determine how much time might be contemplated as necessary or required even for that purpose alone."

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But Lord Pannick had already acquiesced to the idea that a prime minister could use prorogation for political gain.

In the example stated as the government's motive - that it needs extra time to prepare a Queen's Speech - this does in essence give them a political advantage.

But where it is argued the prime minister has crossed the line, according to the appellant, is where it undermines parliamentary sovereignty.

If this was his motivation then it goes beyond political advantage and into the realms of a power grab.

Image: Boris Johnson has insisted the UK will leave the EU on 31 October

Indeed, it was pointed out that even if it wasn't intended - but still had that effect - then it would be improper, as ruled by the Scotland's Court of Session.

Lord Pannick argues that the PM has actually given away what his motive is in a Sky News interview.

Speaking to Sky's political correspondent Sam Coates, Mr Johnson said: "I'm afraid that the more our friends and partners think at the back of their minds that Brexit could be stopped, that the UK could be kept in by parliament, the less likely they are, to give us the deal that we need and so that's why I really hope that MPs will allow the UK to do a deal and get ready for a no-deal Brexit."

That he had a motivation, doesn't mean it was his motive.

We'll know by the end of the week whether any of this convinces the judges that the prime minister did indeed lie to the Queen about why he wanted MPs to take a five-week break.