It’s been a while already, but I would like to say a few things about the UK Supreme Court’s decision that Prime Minister Boris Johnson’s advice, last moth, that the Queen prorogue the Westminster Parliament for five weeks was unlawful, and that the prorogation is a nullity. The unanimous decision by Lady Hale and Lord Reed, R (Miller) v Prime Minister,  UKSC 41 (Miller (No 2)) breaks new and, in my view, shaky constitutional ground. It is an understandable response to what Lord Sumption has accurately described as Mr. Johnson’s “constitutional vandalism”. But, while understandable, I am not persuaded that it is right.
I should note, of course, that I am no great expert on UK constitutional law. Many people who are have written about Miller (No 2) already, but, due to my recent travels and speaking engagements, I haven’t been able to keep up with the torrent of commentary. Anyway, the principles at stake are similar to those that apply in Canada and New Zealand, and I wanted to produce a record of my own thoughts regarding Lady Hale and Lord Reed’s reasoning. Add salt to taste. I will also add a note on the applicability to this decision to Canada, where of course the ability of a Prime Minister to procure the prorogation of Parliament for political purposes is something that has already been done, and could be attempted in the future.
The substantive issue in Miller (No 2) was whether the Prime Minister’s advice that the Queen prorogue Parliament for a five-week period was unlawful, either because it interfered with the constitutional principles of Parliamentary sovereignty and government accountability to Parliament, or because it had an improper purpose. But as a preliminary matter the Court had to decide whether the matter was justiciable at all. If it found that it was, and that the prorogation was unlawful, it also had to consider the appropriate remedy.
The argument against justiciability was that the substantive issues were subject to political accountability rather than judicial scrutiny and that there were, in any case, no legal criteria by which the lawfulness of advice to prorogue Parliament could be determined. For the judiciary to step into this controversy would offend against the separation of powers. But the Court rejected this contention. The fact that the decision it was asked to review was made by a political actor, had political resonance, and was potentially subject to political accountability did not, without more, mean that courts should refrain from reviewing its legality. As for the separation of powers, it would only be enhanced “by ensuring that the Government does not use the power of prorogation unlawfully with the effect of preventing Parliament from carrying out its proper functions”. 
The power to prorogue Parliament is based in the Royal prerogative; that is to say, it is a power of the monarch that is recognized by the common law (rather than having a statutory foundation). The common law also outlines the limits of prerogative powers. Doubts about justiciability, the Court says, can legitimately arise if the dispute concerns the lawfulness of the exercise of a prerogative power within its proper limits. However, there is no question that it is the courts’ role to draw the limits in the first place. The dispute here, the Court says, involves just this sort of line drawing.
How are the limits of a prerogative power to be ascertained? Unlike with a statutory power, there is no text to guide the court. However, the scope of any prerogative power “has to be compatible with common law principles”, including “the fundamental principles of our constitutional law”,  which, despite the fact that the UK’s constitution is not codified and consists of “common law, statutes, conventions and practice”, “are enforceable by the courts in the same way as other legal principles”. 
Two such principles help circumscribe the scope of the power to prorogue Parliament: Parliamentary sovereignty, and the accountability of government to Parliament. The former means not only “that laws
enacted by the Crown in Parliament are the supreme form of law in our legal system”  but also that the executive cannot get int the way of Parliament “exercis[ing] its legislative authority”  as it would be in the absence of limits on the power of prorogation. While prospect of unlimited prorogation may be hypothetical and subject to “practical constraints”,  its very existence would be incompatible Parliamentary sovereignty, and therefore intolerable. The same goes for the accountability of the Ministry to Parliament,
through such mechanisms as their duty to answer Parliamentary questions and to appear before Parliamentary committees, and through Parliamentary scrutiny of the delegated legislation which ministers make. 
This accountability serves to ensure that “citizens are protected from the arbitrary exercise of executive power”,  but it too would be undermined by long-term prorogations.
It follows then that, while a short period of prorogation is acceptable as not interfering with Parliament’s legislative power or its scrutiny of the executive, the longer Parliament stands prorogued, the more these principles are put at risk. There is no bright-line limit between what is and what is not lawful. Rather,
a decision to prorogue Parliament (or to advise the monarch to prorogue Parliament) will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive. 
Whether a given prorogation has this effect, and whether, if so, a justification has been provided for it, are questions of fact of “no
greater difficulty than many other questions of fact which are routinely decided by the courts”.  The court must decide these questions “with sensitivity to the responsibilities and experience of the Prime Minister, and with a corresponding degree of caution”,  but it can and must decide them. In this case, the Court finds that the length of the prorogation will interfere with Parliamentary sovereignty and the accountability of government, and that the justifications advanced on behalf of the Prime Minister are unpersuasive. Its decision on the latter point is influenced by the evidence given by a former Prime Minister, Sir John Major.
The Court must, then, decide on the remedy. The applicant would have been content with a declaration to the effect that the Prime Minister’s advice to prorogue Parliament was unlawful, but the Court goes further. Having rejected the contention that the prorogation is part of “proceedings in Parliament” whose validity the courts are precluded from reviewing by Article 9 of the Bill of Rights 1688, it finds, that the Order in Council signed by the Queen to require the prorogation,
being founded on unlawful advice, was likewise unlawful, null and
of no effect and should be quashed. This led to the actual prorogation, which was as if the Commissioners had walked into Parliament with a blank piece of paper. It too was unlawful, null and of no effect. 
The prorogation never happened.
As noted above, one can understand why the Supreme Court decided the way it did. Indeed, the reasoning of Lady Hale and Lord Reed has a certain elegance to it, and I think it is fair to say that a constitution in which the power to prorogue Parliament cannot be abused for partisan or political purposes is preferable to one where it can be. It would indeed be shocking if the Prime Minister were to attempt proroguing Parliament for years on end. As Canadians will recall, it is equally shocking when the Prime Minister uses a prorogation to avoid being held to account by Parliament. The question, though, is whether the United Kingdom actually had such a constitution, prior to the Supreme Court’s decision in Miller (No 2).
Canadians, of course, will be interested in what our constitution has to say on this. Let me begin with that. Unlike the United Kingdom’s, Canada’s constitution is partially codified and entrenched. As it happens, this entrenched constitution includes a specific provision that speaks to the possibility of indefinite prorogations: section 5 of the Canadian Charter of Rights and Freedoms provides that “[t]here shall be a sitting of Parliament and of each legislature at least once every twelve months”. An attempt to prorogue Parliament, or a legislature, for more than a year would be flatly unconstitutional, and a court ought to be able to recognize this and, pursuant to section 24(1) of the Charter, provide any “such remedy as the court considers appropriate and just in the circumstances”.
But what about abusive attempts to prorogue Parliament for periods of time shorter than a year? In my view, the Charter settles this matter differently than the common law constitution of the United Kingdom. Instead of a standard of justification, as under the latter, the Charter sets out a bright-line rule, and it would be inappropriate for the courts to re-write the constitution that we actually have in order to improve it on a pattern suggested, decades after its enactment, in a jurisdiction whose own constitutional landscape is, on this point, somewhat different from ours. The Supreme Court of Canada rejected an attempt to invoke constitutional principles to add to the Charter’s proscription on retroactive criminal law in British Columbia v Imperial Tobacco Canada Ltd., 2005 SCC 49,  2 SCR 473, and it should follow the same logic in rejecting an attempt to import Miller (No. 2) into Canadian law.
This is not to say that the one-year line drawn by the Charter‘s framers is especially satisfactory. Certainly shorter prorogations can be abusive, as we saw in 2008. Perhaps our constitution could be improved by an amendment to section 5 of the Charter, just as it would in my view be improved by an expanded proscription against retroactive legislation. But of course such an amendment is not for the courts to effect. And, as I will now suggest, it is not obvious that such an amendment ought simply to codify the Miller (No. 2) decision.
Indeed it is not clear that the authors of Miller (No. 2) viewed it as a model for anything else that would follow. At the outset, the insist that the case “arises in circumstances which have never arisen before and are unlikely ever to arise again. It is a ‘one off'”.  It is worth pointing out that this is an unusual statement for a court to make, and it should, I think, ring some alarm bells. (Consider another instance where a court said something similar: Bush v Gore, 531 US 98 (2000) where the per curiam majority opinion noted that its “consideration is limited to the present circumstances”. (109))
At the very least, one suspects that, despite its confident assertions about its ability to resolve factual claims about the necessity for a prorogation, the Court probably hopes that it will not have to do so again. And, perhaps even more fundamentally, the Court may well realize that it has not really articulated a principle against which to judge the lawfulness of prorogations so much as asserted the power to do so on a case-by-case basis. The Court gets away with it by shifting the burden of proof onto the Prime Minister, who is asked to justify his request for a prorogation instead of the applicants having to actually show that it was flawed in some legally cognizable way (as opposed to “merely” stinking to high heaven). Mr. Johnson was not prepared to discharge the burden. His successors, presumably, will not make the same mistake.
Seen in this light, Miller (No. 2) looks less as a re-assertion of constitutional principle in the face of a band of governing vandals, and more like a power grab. The vandals, admittedly, are real, so the power grab is for a good cause, but it’s a power grab all the same. This impression is only reinforced by the way in which the Court re-framed the issue from the legitimacy of a particular (albeit disturbing in the extreme) exercise of an undoubted prerogative power (namely, that of proroguing power) to that of the scope the prerogative. The cases on which the Supreme Court purports to rely sought to preserve a space for the exercise of prerogative powers that would not be amenable to judicial review, being too bound up with issues of policy and politics. Miller (No. 2) does not repudiate these cases, but it suggests a way around them: it is enough to say that, correctly understood, the issue concerns the scope of a prerogative power rather than the lawfulness of its exercise within its acknowledged scope.
If the prerogative of dissolution had not been abolished in the UK, this trick could have been applied to engage the courts in reviewing its exercise. (Of course, this prerogative has been preserved in Canada, even in jurisdictions that have adopted purportedly fixed election dates; this is an additional consideration that ought to give pause to Canadian courts urged to import the Miller (No. 2) reasoning here.) The same goes for the prerogative of mercy and the prerogative powers in relation to foreign affairs or war. In fairness to the Supreme Court, I doubt that it really wants to go there. If urged to embark on this sort of review, it can still say that, this time, the issues do not go to the scope of the prerogative. But that only highlights the fact that the reasoning in Miller (No. 2) is results-oriented. A one-off indeed. I don’t think this is the stuff of great constitutional law.
There are at least a couple of additional issues worth addressing about Miller (No. 2), one of which I will make here, and the other in a separate post. The former is that the Supreme Court’s conception of Parliamentary sovereignty is, in my view, something of a departure from how this concept has been understood until now. The orthodox view is that it referred to the supremacy of the law enacted by the existing Parliament over any other law ― common law, regulations, and even statutes enacted by Parliaments past. In recent decades, this view has been somewhat tempered by a growing acceptance Parliaments dictating the “fanner and form” ― but not the content ― of future statutes. Of course Parliamentary sovereignty in this orthodox sense is not at all affected by prorogation. But the Supreme Court expands this principle, by saying that it requires that there be no obstacles, or at least no obstacles created by the executive, in the way of a Parliament that might legislate, as opposed to one that already has.
I wonder how much the Court has thought this through. There is a tension between this understanding of sovereignty and the few that Parliament can complicate the life of its successors by enacting “manner and form” requirements. There is an even stronger tension between this view and the musings of some judges (Lady Hale among them!) about the possibility that Parliamentary sovereignty isn’t quite absolute, and that there might be some laws that Parliament cannot enact (or rather, that Courts would be justified in not giving effect to some laws). Again, future courts might resolve this tension by saying that the expanded version of Parliamentary sovereignty is a single-purpose idea meant to control the executive and not the other branches of government. But I wonder whether, in trying to stave of off the absolutist claims of the executive, the Supreme Court hasn’t provided intellectual ammunition for similar claims by Parliament.
The other way in which Miller (No. 2) departs from past, and indeed very recent, understandings of how the UK constitution (and other constitutions derived from it) works, which I will not address in detail here, has to do with the distinction between the legal and the political constitution. This distinction was a sharp one, or so we were told told by writers such as A.V. Dicey and courts in cases like Re: Resolution to amend the Constitution,  1 SCR 753 (Patriation Reference) and R (Miller) v Secretary of State for Exiting the European Union,  UKSC 5 (Miller (No. 1)). Statutes and common law rules were legal and legally enforceable rules; constitutional conventions, political and not legally enforceable. In Miller (No. 2) the lines between these types of constitutional rules are are blurred. This might not be all bad, but I will defer this to a separate post, which I will try to write in a not-too-distant future.
To repeat yet again, I am not criticizing the reasoning in Miller (No. 2) because I approve of, or even regard as at all defensible morally, the actions of the Prime Minister that led to it. The Supreme Court acted out of genuine and perfectly understandable concern with gross abuse of power, for which it found no redress in the orthodox legal toolkit, and so took unorthodox measures. As H.L.A. Hart wrote long ago, in cases where constitutional fundamentals are at stake, courts can reshape them and so transform our understandings of what law even is; “all that succeeds”, he observed, “is success”. Clearly, the UK Supreme Court has been successful. And perhaps that’s all that history will remember.
But the price of present success is, at best, considerable uncertainty about the future. Will the reasoning in Miller (No. 2) ever be followed, and if so, to what end? Will it serve to involve the courts in review of deeply political decisions about foreign affairs, war, and peace? Will the expansion of the understanding of Parliamentary sovereignty rebound it ways we may yet regret? Again, I wonder how much the Supreme Court ― pressed for time as it was, and apparently hoping to deliver a “one off” decision ― has really pondered all this. We, at any rate, have the leisure ― and the need ― to reflect on what it has done.