I wrote last week about the UK Supreme Court’s decision in R (Miller) v Prime Minister,  UKSC 41 (Miller (No 2)), which unanimously held that the Prime Minister’s advice that the Queen prorogue Parliament for five weeks was unlawful, and the prorogation itself, therefore invalid. There was, however, one aspect of Miller (No 2) that I did not discuss in any detail: that of the Court’s treatment of the “political constitution”, and the distinction between those constitutional rules that are part of constitutional law and those that are not. In this post, I want to come back to this issue.
It is useful to begin with the orthodox view of the political constitution, articulated by scholars 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)). On the orthodox view, only some constitutional rules ― statutes and common law rules, such as those circumscribing the scope of the royal prerogative and, in part, of Parliamentary privilege ― are part of constitutional law. Other rules, known as constitutional conventions, are not constitutional law and the courts will not enforce them, although they can sometimes take note of them in resolving properly legal issues.
In the Patriation Reference, the Supreme Court of Canada suggests a number of reasons for distinguishing convention and law. First, the majority opinion on the conventional question insists that “unlike common law rules, conventions are not judge-made rules. They are not based on judicial precedents but on precedents established by the institutions of government themselves.” (880) The majority opinion on the legal question makes the same point, and adds that “[t]he very nature of a convention, as political in inception and as depending on a consistent course of political recognition … is inconsistent with its legal enforcement”. (774-75) In Miller (No 1) the majority of the UK Supreme Court put it more pithily: “[j]udges”, it said, “are neither the parents nor the guardians of political conventions”. 
Second, and relatedly, the Patriation Reference suggests that it would be inappropriate to enforce conventions, given their questionable pedigree. “What is desirable as a political limitation ”, it says, “does not translate into a legal limitation, without expression in imperative constitutional text or statute”. (784) Third, the majority opinion on the conventional question argues that the courts lack remedies to compel compliance with conventions. Fourth and last, the same opinion notes that conventions conflict with legal rules, and courts are bound to apply the latter. Others have also argued that conventions are too shrouded in uncertainty―that both their very existence and their implications for specific situations are too doubtful―for them to function as meaningful legal rules.
Miller (No 2) doesn’t explicitly engage with any of this. But by the time the UK Lady Hale and Lord Reed are done with the case, not much of the old orthodoxy is left standing. They not only regularly advert to conventions (which courts can do on the orthodox view), but seem to assimilate the exercise of conventional and legal powers, and arguably provide a way for judicial enforcement of conventions, in disregard of the traditional distinction between conventions and law. This might be a good thing, but I am uneasy at the way it is accomplished.
The tone is set early on. At the beginning of the judgment, Lady Hale and Lord Reed explain what a prorogation is, and contrast it with a dissolution of Parliament. Following the latter, they note, “[t]he Government remains in office but there are conventional constraints on what it can do during that period”.  There is no particular need to mention these “conventional restraints”, even for the sake of the descriptive point the Court is making (which is itself unnecessary, although perhaps helpful, to explaining the decision in the case at bar). A more orthodox court would probably have avoided mentioning conventions here. Not this one.
More relevantly to the case, Lady Hale and Lord Reed say that they “know that in approving the prorogation, Her Majesty was acting on the advice of the Prime Minister”.  They go on to further explain that
the power to order the prorogation of Parliament is … exercised by the Crown, in this instance by the sovereign in person, acting on advice, in accordance with modern constitutional practice. It is not suggested in these appeals that Her Majesty was other than obliged by constitutional convention to accept that advice. 
The double negative allows the judgment to ostensibly “express no view on”  whether Her Majesty was indeed “obliged by constitutional convention” to accept the Prime Minister’s advice, but the fig leaf is quickly blown away. The Court proceeds to assess the lawfulness of the Prime Minister’s advice, which makes little sense unless one assumes that Her Majesty had to follow it. If the advice was in reality what it is in name, why would the Court be looking into it? This is further confirmed by the Court’s approach to the remedy. The applicants’ lawyers, implicitly adopting a more orthodox position, only sought “a declaration that the advice given to Her Majesty was unlawful”.  But the Court goes further, and says that this advice “led to the Order in Council [pursuant to which the prorogation was carried out] which, being founded on unlawful advice, was likewise unlawful, null and of no effect and should be quashed.”  Led to? Founded on? This, I am tempted to say, is an imitation fig leaf, not even the real thing. What Lady Hale and Lord Reed mean ― the only way they reasoning makes sense ― is that the advice required the order in council to be made; that it was legally determinative, not just factually causative.
Consider: If I write a letter to Boris Johnson with a devious master plan for executing no-deal Brexit, and he follows it to the letter, my letter, which will actually be advice, in the sense of a suggestion, will not be the subject of court proceedings. The relevant choices will still be the Prime Minister’s, and, should their legality be called into question, my intervention will be no more than a part of the factual background, if that, even though it would be fair to describe it as “leading to” the Prime Minister’s actions, which would be “founded on” it. Of course, my position vis-à-vis the Prime Minister is different, in a constitutionally significant way, from the Prime Minister’s vis-à-vis the Queen. But, on the orthodox view, this would significant as a matter only of political, not legal, constitutionalism. The Supreme Court sees things differently. To repeat, Lady Hale and Lord Reed’s approach only makes sense if the Prime Minister’s advice is binding on Her Majesty, so that there is no daylight between his ostensibly conventional role and the exercise of the Crown’s legal powers.
Perhaps one might argue that the UK Supreme Court’s treatment of conventions is orthodox because it is only a necessary step towards resolving a properly legal question as to the scope of the prerogative power of prorogation. The Court, on this view, does not do what the Diceyan dogma tells us is impossible: enforce a convention. But is that so? And if it is so in this case, what about others in which the Court’s reasoning might be applied? (As discussed last week, the Court claims that Miller (No 2) is a “one off”. That remains to be seen.)
It is crucial, I think, to Lady Hale and Lord Reed’s reasoning that they are able to confidently assert that, while “Parliament does not remain permanently in session … [i]n modern practice, Parliament is normally prorogued for only a short time”.  They rely, moreover, on a statement by a former Prime Minister to the effect that nothing more is necessary. And they conclude that constitutional principles (specifically, Parliamentary sovereignty and executive accountability) mean departures from modern practice would require justification. Without explicitly undertaking an analysis in terms of the Jennings test adopted by the Supreme Court of Canada in the Patriation Reference, Lady Hale and Lord Reed come close to showing that the relevant constitutional actors seem to be following a rule, that they feel bound by the rule (or at least that they have no reason not to follow it), and that there are reasons, in the shape of important constitutional principles, for this rule ― in other words, that, according to the Jennings test, there exists a convention. Only, in effect, Miller (No. 2) very nearly transmutes this “modern practice” into law. (Very nearly, because in principle it is still open to a Prime Minister to justify departure from the practice.)
And beyond what has or has not happened in this particular case, I think the reasoning deployed by Lady Hale and Lord Reed can serve as a blueprint for judicial enforcement of conventions in the future. In a nutshell, what Miller (No 2) says is that the exercise of the royal prerogative is subject to implicit limits imposed by constitutional principles, and that the location of these limits ― which can be inferred, in part at least, from “modern practice” ― is a justiciable question. So consider, for example, the convention requiring the sovereign to assent to legislation passed by the House of Commons and the House of Lords (or only the House of Commons legislating pursuant to the Parliament Act 1949). Courts couldn’t enforce that convention and either require the sovereign to assent or treat a bill passed by the Commons and the Lords as law without her assent, right? Well, they could say that the power to withhold assent is subject to implicit limits imposed by the democratic principle, such that any departures from the modern ― or, this case, centuries-old practice of not withholding assent ― must be justified, and… voilà!
As readers may know, I am a longtime skeptic of the Diceyan orthodoxy on the separation between conventions and law. I think that the courts should have regarded conventions as common law rules en devenir and enforced them if and when necessary, subject however to justiciability concerns ― for example when the conventional rule is vague and/or its application in a given case involves political judgment. So the outcome of Miller (No 2) is not all bad, from that perspective.
And its reasoning makes the arguments invoked in support of the orthodoxy that much more difficult to sustain. The emphasis that Lady Hale and Lord Reed put on the development of the common law constitutional rules in cases such as the Case of Proclamations shows that the disclaimers of the creative role of the judiciary and protestations about its inability to translate “what is desirable as a political limitation” into legal rule always proved too much. Similarly, their confident treatment of the question of the remedy and of the evidentiary issues shows that concerns about the courts’ ability to engage with conventional issues have been greatly exaggerated.
That said, I have my reservations about the approach the Miller (No 2) court takes. For one thing, I wish Lady Hale and Lord Reed had been more transparent about what they were doing. Miller (No 1), where the UK Supreme Court reiterated the orthodox view that a convention could not be judicially enforced ― even a convention enshrined in statute! ― was only decided a couple of years ago. Miller (No 2) is almost a complete U-turn from its namesake, yet we have little explanation about why the ladies and lords were for turning. Here as on other issues, the suspicion of results-oriented reasoning must weigh heavily on the Court. More substantively, Lady Hale and Lord Reed may be overconfident in the courts’ ability to dispose of the factual questions that may arise when the courts enter the realm of politics. As noted above, I think that these questions will sometimes ― though by no means always ― be difficult enough that non-justiciability is a real concern. The reasoning in Miller (No 2) does not acknowledge this, and in my view this is a mistake.
Miller (No 2) thus seems to be a very significant, albeit unacknowledged, development in the UK Supreme Court’s understanding of the nature of the constitution, and specifically of what used to be thought of as its political, non-legal component. Without saying so, the Court is, perhaps, in the process of correcting the mistake made by scholars and judges who saw a sharp separation between law and politics when, at the heart of the UK’s constitution, none existed. Views on the nature and status of conventions that were just recently said to be quite heretical now appear to have prevailed.
If anything, the pendulum may have swung too far in the other direction. The Court hasn’t thought through the implications of its reasoning. Perhaps this is just how the common law develops: case by case, without the courts fully understanding the consequences of one decision for those that will follow. In that sense, Miller (No. 2) might not be an innovation at all. The system works, perhaps, but it is not always a pretty sight.