Thread by @BBCDomC

Ok we're now underway. Starting with Lord (David) Pannick QC for Gina Miller. Reminder - she lost at the English High Court. Her argument is that the PM prorogued Parliament for a longer period than usual to prevent discussion of his Brexit policy.

He says the Prime Minister's prerogative power has been misused to prevent Parliamentary debate of Brexit. The PM's prerogative power is accountable to Parliament - but he has used it to try to evade being held accountable.

"It conflicts with the basic principle of our constitutional law." Prerogative powers are subject to the powers of a democratically-elected Parliament, he says.

Lord Pannick for Gina Miller says the High Court got it wrong in deciding prorogation was a purely political question. The court is being asked to answer the legal question: is it within the scope of the PM's power for him to close Parliament [to prevent debate].

Pannick QC: "When the PM exercised his broad discretionary power to advise the Queen, it is an improper purpose for him to wish to avoid Parliamentary control over the policies of his government."

"The length of the prorogation is relevant because the exceptional length is strong evidence that the PM's motive was to silence Parliament because he sees Parliament as an obstacle."

Lord Pannick tells Lady Hale & the 10 other justices that they have a "common law duty" to intervene if the PM has used his power improperly. "It's very far from academic that Parliament is unable to conduct such business [on Brexit] that it thinks is appropriate."

Now, put briefly, the government says there is no legal precedent permitting the court to get involved. Lord Pannick says there is no precedent because no Prime Minister in modern times has allegedly abused his powers in such a way.

We've reached a moment of muddle over the numbering of pages in the legal bundles. If you got "22 minutes" in that particular sweepstake, the drinks are on you.

Lord Pannick quotes from a BBC interview with Mr Johnson in which he says: "The best way to leave with a deal is if our friends and partners over the channel don't think that Brexit can be blocked by Parliament."

Pannick says this interview and another on Skyy are "strong evidence" of the prime minister's motive to close Parliament for five weeks while he attempts to extract a new deal from Brussels.

IMPORTANT: It’s now emerged that the Prime Minister has not made a witness statement explaining why he advised her Majesty to prorogue Parliament for five weeks.

Such a witness statement to court - had it emerged - would have been subject to the standard rules of being truthful - Lord Pannick notes that telling porkies in witness statements is an offence.

(To be clear - this issue has been previously raised in the lower courts. Lord Pannick's point is the PM has not provided such a statement to assist the Supreme Court. Apols if that was not clear)

“We say this case cries out for a witness statement from the Prime Minister," he says, adding the Prime Minister should have submitted himself to potential cross-examination.

Lord Pannick: The #supremecourt should draw an inference about the PM's motives because of the absence of material setting out what he says he was up to. He wouldn't have recommended a 5-week prorogation were it not for his desire to close down Parliamentary debate of Brexit.

Bit early to read the runes, but we've had three interventions/questions so far from Lords Carnwath and Reed. They were two of the three dissenting judges in the court's decision that Parliament, not the PM, has the power to trigger Art 50 and leaving the EU.

Ok back to Lord Pannick. He is now focusing on the material effect of proroguing Parliament and the interference with its sovereignty. Prorogation means MPs can’t ask any questions of ministers, debate events, pass law & hold govt to account.

Lady Hale, the court’s president, says the justices want to know what Parliamentary bills have been lost by being closed for five weeks. This is interesting. It indicates they may be considering not just the PM’s “intention” but its “effect”.

The answer is apparently 13 bills - HT to @Greg_Callus for tweeting the link: theparliamentaryreview.co.uk/news/prorogati…

Lord Pannick says that the purpose of the PM - or "inevitable effect" - is to "silence Parliament and undermine constitutional principle.” That constitutonal principle is Parliamentary sovereignty.

Quoting from the outcome of the Article 50 challenge, Lord Pannick has set out the UK's constitutional settlement. In essence, when a minister uses their executive, or prerogative, powers they remain answerable to Parliament.

"Ministers are constitutionally the junior partner - and the real issue in this case is whether the junior partner may lawfully remove the scrutiny of his activities by the senior partner [Parliament].”

Run of quotes from Panick as he hammers home his argument - this is really interesting:

"The basic principle is that Parliament is supreme. The executive is answerable to Parliament…

"Parliamentary sovereignty is not confined to cases where the executive frustrates an Act of Parliament - it must also apply to cases - and this is a unique case - where the executive takes a decision with the purpose or effect of removing the ability of Parliament to legislate."

"Indeed it could be a greater breach of Parliamentary sovereignty to prevent Parliament from legislating as it sees fit than for the executive to defy a particular law...

"The inferior body, the junior body, cannot use its constitutional powers to prevent the superior body from performing its constitutional functions particular when he constitutional function is the scrutiny of the junior partner itself.”

Important question from Lord Hodge: Can the PM use prerogative power to prorogue Parliament in pursuit of “political advantage”?

Pannick QC for Gina Miller says a PM cannot shut down Parliament for political advantage if it means shutting down scrutiny in the current manner.

Panick: "The Prime Minister cannot [as a matter of law] have discretion as to the breadth of the powers that he enjoys.”

In final 10 minutes of session, Lord Pannick turns to government’s key argument - that the case cannot even be considered by judges. Tactically, he is trying to diminish its importance - he wants the court to focus on PM’s intention and its effect on Parliament’s sovereignty.

No surprise, he cites lots of case law arguing judges have the power to scrutinise ministerial prerogative powers which are not limited by clear acts of Parliament.