Should the Supreme Court declare the advice by the Prime Minister to the Queen to prorogue parliament unlawful? In my view no.
The prorogation power, although politically misused in this case, falls within the exclusive purview of parliament.
For courts to rule on its exercise would lead them into the exclusive jurisdiction of Westminster, interfering in the deep political relationship between Crown and parliament that is the fundamental hallmark of our system of government.
At the heart of this case is a misconception regarding the nature of the British constitution. The issue is frequently presented as a battle between the Crown (as government) on the one hand and parliament as law-maker on the other.
In fact, the British constitution has no such separation of executive and legislative powers.
The supremacy of law in our system is encapsulated in the intimate relationship between these two institutions: the sovereignty of the Crown-in-Parliament.
The Crown as executive sits in parliament and is accountable to parliament every day through questions, debates and committees.
The government introduces the vast bulk of legislation which parliament then enacts, with the consent of course of the Crown.
Not only are the Crown and parliament not separate; without this deep level of institutional interaction our parliamentary system of government, shared by much of the Commonwealth, would make no sense.
It is no surprise therefore that some of the most surprised responses to the Scottish Court of Session decision have come from Canadian observers.
In Canada, even with a written constitution, the prorogation power is understood to be firmly part of the political constitution and beyond the reach of judges.
Prerogative powers are central to the effective operation of this relationship of supremacy between Crown and parliament.
These are the ancient, residual powers of the constitution that have not been removed by parliament precisely because they facilitate its status as the pinnacle of the British legal order.
Prorogation is one of these, as is the Queen’s authority to grant Royal Assent to legislation and to appoint and dismiss ministers on the advice of the Prime Minister.
Together these ‘prerogatives of sovereignty’ are the essential political machinery that makes our system work and which allows for deep political contestation within the Palace of Westminster, unhindered by legal constraints.
How can we be so sure that parliament approves of the Crown’s exclusive power to prorogue parliament? The answer is straightforward.
Parliament has the power to make any law. It can legislate to curtail or remove prerogative powers altogether, and frequently does so.
The prerogative power to dissolve parliament, by which a Prime Minister could advise the monarch to call a general election at will, has been limited by the Fixed Term Parliaments Act.
Crucially, by contrast, the prorogation power has not been subjected to any such limitation. Parliament has had three hundred years to constrain this power but has chosen not to do so; in the FTPA it expressly excluded prorogation from legal controls.
In the time available to parliament before prorogation took place it could have legislated to prevent it. Legislation is superior in law to prerogative powers; such a statute would have stopped prorogation dead in its tracks.
Why did it not do so? One reason is that parliament is of course deeply divided over whether this particular prorogation decision is correct or not.
More fundamentally, far from being a power that threatens parliament, the prerogative of prorogation, and its insulation from judicial oversight, is a power that confirms the legislature’s very independence.
The Crown-in-Parliament is the ultimate law-making power in the land; part of that power includes exclusive jurisdiction over the functioning and sitting of parliament itself.
If the courts venture into the realm of parliament’s workings they threaten the very source of sovereignty which is the essence of the British unwritten constitution.
The present case is part of a trend that seeks to bring matters relating to Brexit before the courts.
Petitioners are of course entitled to find legal arguments where they can. But the courts should be wary if they are being weaponised by one side of an essentially political dispute.
One consequence could be a proliferation of ‘political cases’; we could well see a spate of actions brought by Brexiteers should the balance of political power shift after the next general election.
None of this is healthy.
Judges must do justice according to law but they should also be circumspect when they sense that law is being used as a political tool.
The unedifying spectacle last year of America descending into a culture war over the appointment of Justice Brett Kavanaugh to the US Supreme Court was a timely reminder that one advantage of our unwritten constitution is that political value judgments do not rest in the hands of judges.
In general we consider our senior judges to be impartial referees; Americans see theirs as politicians in robes. Judges in the UK are wise to guard their impartiality carefully.
Cases such as these are a political minefield and reinforce the importance of appropriate judicial restraint.
The decision by the Prime Minister to seek prorogation was extremely ill-advised.
It seems highly likely that the closure of parliament was sought for an ulterior purpose than that publicly stated, bringing the Queen into the political arena in a most unfortunate way. If this is the case we can say that the Prime Minister acted unconstitutionally.
However, he was called to account for this and widely criticised in parliamentary questions and debate before prorogation took place; when parliament reconvenes, and regardless of the outcome of the current case, he will no doubt face further political opprobrium.
It will also be open to parliament to curtail by way of legislation the prorogation power as it has limited the dissolution power.
This is how it should be.
If convention has been broken parliament should make clear its disapproval and seek to prevent it from happening again.
But ultimately this is a matter of political judgment that must be dealt with by our supreme and elected political institution; it is not a matter for the courts.
By Professor Stephen Tierney, Professor of Constitutional Theory and Director of the Edinburgh Centre for Constitutional Law. This article was originally published by the Telegraph.