WHAT is prorogation? What is the Court of Session case challenging it all about? And what are its chances of success?

Let’s tackle prorogation first. At its simplest, prorogation suspends parliamentary sitting. The consequences of this are far reaching.

Prorogation slams shut the old parliamentary session. This liberates a government from ongoing scrutiny by MPs. Motions can’t be lodged and voted upon. Committees don’t sit. Bills and amendments can’t be considered. Parliamentary questions can’t be asked or answered.

Significantly, prorogation also has the effect of wiping the parliamentary slate clean. Unanswered questions to ministers can now be ignored. Unfinished legislative work is dumped and has to be restarted anew in the next session.

This is particularly significant in the context of Brexit. On agriculture, on immigration, on fisheries, the Government has several unfinished bills wending their way through parliament to provide legal frameworks for some areas of UK law post-Brexit. Prorogation immediately wipes these bills out. The UK Government claims it is giving its all to No-Deal preparations. This cynical prorogation gives the lie to this boast, as several of the falling bills represent concrete ways of handling a bumpy transition out of the European Union.

For Boris Johnson’s administration, the proposed prorogation is both a sword and a shield. It protects the Government from five weeks of scrutiny, while disarming the internal and external opposition to his policy of critical Commons resources. From the perspective of frustrating a No-Deal Brexit, prorogation makes it extremely difficult for opposition MPs to get their act together in time.

So what about the court case? For context, this is a judicial review action. In Scotland, these can only be brought at the Court of Session in Edinburgh. Heard first by a single judge of the Outer House, either side will be able to appeal this judgment first to at least three judges of the Inner House of the Court of Session, followed potentially by a jaunt to the Supreme Court in London.

Judicial review actions are – essentially – about the rule of law. The court exercises a supervisory jurisdiction, ensuring that decision-makers who have been given legal powers observe the limits of those powers and act fairly.

Let’s be clear about what did and didn’t happen this week. In the immediate aftermath, some reports suggested Lord Doherty had rejected the substance of the challenge and had found “Boris Johnson can prorogue parliament”. Not so. On Friday, the judge took two important decisions. Firstly, he expedited the full hearing to next Tuesday. Secondly, he knocked back the petitioners’ application for an interim interdict.

An interdict, essentially, is an order not to do something. The court can refuse interim interdicts where there is clearly no merit to a case, or where the balance of convenience points against making orders before the merits of the case have been fully heard. Lord Doherty’s decision on Friday was taken under the second heading. With a full hearing scheduled for next week, there was no pressing need to make an order on Friday. Boris Johnson isn’t going to prorogue parliament over the weekend.

So what’s the key argument the court will consider next Tuesday? In lawyer speak, the petitioners are arguing that the proposed prorogation of Parliament is ultra vires. In more conventional terms, they are arguing it is unlawful. But how, and why? After all, as defenders of the Government have been quick to point out, prorogations between parliamentary sessions happen all the time. On paper, the constitutional principles informing the decision seem pretty clear.

The power to prorogue parliament is part of the royal prerogative. Memorably criticised by Tory MSP Adam Tomkins in a past life as “elastic and ill-defined powers”, arcane and archaic, prerogative powers are the residual powers of the monarch, which she now exercises on the advice of her ministers – even when those ministers do not have a Commons majority at their back.

Prerogative powers don’t derive from any Act of Parliament, though they can be removed and regulated by them.

Historically, it was the royal prerogative which gave the sitting prime minister the power to spring General Elections on their opponents whenever the winds of politics seemed most favourable to their interests.

That power has been trimmed back by the Fixed-term Parliaments Act, but other significant prerogative powers have been retained.

These aren’t just constitutional bagatelles. Although in recent years Britain’s wars have been endorsed by majority votes in the House of Commons, the Government retains the power unilaterally to declare war through the prerogative.

If he hadn’t carried a majority of the Commons into the folly of the Iraq War, in law, Tony Blair could nevertheless have unleashed the RAF on Baghdad and Basra. When David Cameron lost his Commons vote on attacking Syria in 2013, only politics constrained the Prime Minister from launching the missiles into Damascus and Aleppo anyway.

Nobody is disputing that the Government has the constitutional authority to recommend to the Queen to prorogue parliament. But, argue the 76 petitioners, the Government’s intentions in doing so matter.

The courts have long recognised that the legality of decisions of ministers and officials can be undermined if they’re based on irrelevant or illegitimate factors.

Take one simple example. A local planning committee may have the legal power to grant or refuse planning permission to an applicant who wants to stick a conservatory on the back of their bungalow. But if it comes to light that planning permission was refused in a particular case only because the applicant was a political opponent of the committee chairman, then the courts could be expected to step in to quash the decision as unlawfully taken.

The detail of the prorogation case is a wee bit more complex, but the petitioners’ argument roughly parallels this example. Their key point is this: when parliament passed the European Union (Withdrawal) Act in 2018, it gave MPs the responsibility to scrutinise – and vote to approve or reject – any “negotiated withdrawal agreement and the framework for the future relationship” with the EU on a motion moved by a Minister of the Crown.

The petitioners argue that the real purpose of shuttering parliament for more than a month is to ensure an automatic No-Deal exit from the EU by compressing parliamentary time to such an extent that MPs’ EU (Withdrawal) Act responsibilities are rendered inoperative.

If this is the Prime Minister’s real intention, they argue, then Boris Johnson is just like the planning committee chair who takes illegitimate factors into account in refusing planning permission to a political foe. Both abuse their powers unlawfully. In these circumstances, the courts have not only the right and opportunity, but the duty to step in to prevent this prorogation from happening.

For their part, Boris Johnson and his ministers have taken to the airwaves to deny any such nefarious intent. The official Downing Street spin was that the decision will enable the Prime Minister to put a fresh domestic programme in front of MPs for debate and scrutiny while also ensuring that there is good time before and after the European Council for parliament to further consider Brexit issues.”

But is this true? Do you buy it? Does anyone? Even ardent Brexiteers seem to assume their Prime Minister is lying to the public about the real reasons for proroguing parliament. They don’t appear to mind the lie. The hearing next Tuesday will determine whether the Court of Session can thole it.