The following is my detailed, initial analysis of the Supreme Court’s judgment in the Cherry/Miller (No 2) case. For a shorter explanation of the case, see this 1,000 words post.
Reactions to the unanimous Supreme Court judgment in Cherry/Miller (No 2)  UKSC 41 have been as strong as they have been diverse. On one analysis — including, arguably, the Court’s own — the judgment amounts to nothing more than an affirmation and application, albeit in a politically fraught context, of orthodox constitutional law. On other views, the judgment breaks new legal ground — and, depending on one’s perspective, in doing so either strikes a much-needed blow for constitutional principle or results in wholly improper judicial interference in the political arena. Against this background, this post considers four respects in which the judgment might be argued (in either positive or pejorative terms) to be novel. I suggest that the better view is that while the judgment develops and applies relevant elements of UK public law in sometimes novel ways — and certainly in novel circumstances — it is rooted in well-established constitutional principles. On this view, the case amounts to a significant restatement of a range of key matters, but cannot justifiably be criticised as having cast aside established principle or as an instance of improper judicial overreach.
Before embarking on that analysis, it may be helpful to summarise the judgment. Following the prorogation of Parliament — a step formally brought about by the Queen on the advice of the Prime Minister — the Court was called upon to determine whether that advice, and the resulting prorogation, was unlawful. As is well known, the Divisional Court had held that this matter was one that a court could not properly consider on the ground that it involved non-justiciable questions. In contrast, the Inner House of the Court of Session considered itself to be under no such inhibition, and concluded that the advice and the prorogation were unlawful on the ground that they had been used improperly so as to “stymie” Parliament from discharging its constitutional functions.
The Supreme Court disagreed with the Divisional Court, holding that the issues raised by the case were properly justiciable. Like the Inner House of the Court of Session, the Supreme Court concluded that the advice and the prorogation were unlawful. However, the Supreme Court reached this conclusion for different reasons. In particular, it held that the prorogation prerogative does not extend to a situation where a fundamental constitutional principle would be impinged upon without a reasonable justification. As the Court put it in a key passage of its judgment:
[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. In such a situation, the court will intervene if the effect is sufficiently serious to justify such an exceptional course.
The Court concluded that no such justification had been offered, given that prorogation of the relevant duration was not necessary to facilitate the Government’s objective of securing a Queen’s speech and a new legislative session. Having reached this conclusion, the Court articulated the logical consequences by confirming that the prorogation was without legal effect and that Parliament therefore remained in session.
A new understanding of parliamentary sovereignty?
The judgment is certainly striking for the way in which it invokes two constitutional principles: namely, parliamentary sovereignty and executive accountability. (In doing so, the Court happily avoided the trap into which it fell in Miller (No 1)  UKSC 5, in which the notion of “constitutional principle” was invoked by the majority in a lackadaisical fashion, often without any adequate attention to what the relevant principles were.) That parliamentary sovereignty is a — if not the — fundamental principle of the UK constitution is entirely uncontentious. What is more novel is the inference that the Court was prepared to draw from the principle of parliamentary sovereignty.
The Court stated, in entirely orthodox terms, that the principle means that “laws enacted by the Crown in Parliament are the supreme form of law in our legal system, with which everyone, including the Government, must comply”. However, while this may be considered the kernel of the principle, the Court went on to say that the principle is not thus confined. Rather, the core principle produces penumbral implications that can themselves properly be thought of as part of the principle of parliamentary sovereignty. This is hardly controversial. Indeed, there are many existing examples of precisely this phenomenon. One such example, as the Court pointed out, is that prerogative power may not be used in ways that are incompatible with legislation enacted by Parliament — a principle established in the seventeenth century in the Case of Proclamations (1611) 12 Co Rep 74, famously applied in the twentieth century in De Keyser  AC 508, and perhaps even more famously applied in 2016 in Miller (No 1) concerning the triggering of the Article 50 withdrawal process. Another implication of parliamentary sovereignty is that Parliament may not bind its successors. A further such implication is one that the Supreme Court had recent occasion to explore in Privacy International  UKSC 22, in which several of the Justices attached weight to the view, expressed by Laws LJ in Cart  EWHC 3052 (Admin), that access to court is a logical corollary of the principle of parliamentary sovereignty, authoritative judicial interpretation and curation of legislation being a prerequisite if Parliament is to have the capacity to enact effective law.
Set against this background and properly understood, the further step taken by the Supreme Court in Cherry/Miller (No 2) is a relatively modest one. That further step entailed holding that the sovereignty of Parliament “would … be undermined as the foundational principle of our constitution if the executive could, through the use of the prerogative, prevent Parliament from exercising its legislative authority for as long as it pleased”. This does not mean that the Court could or should rule, at the level of detail, on what is and is not an acceptable period of prorogation. What it does mean, however, is that it would be incompatible with parliamentary sovereignty for the executive to have legally unfettered authority to prorogue Parliament. A potential response to this argument would be to retort that parliamentary sovereignty requires only that the legislation that Parliament happens to pass should be respected by others, but that the sovereignty principle has no bearing on whether in the first place Parliament has the opportunity to enact legislation. But to advance such a view would be to engage in casuistry. The principle of parliamentary sovereignty is not an arid, technical rule about the hierarchical legal status of legislation enacted by Parliament (albeit that it does make provision in that regard). Rather, it is a fundamental principle that determines and reflects the nature of constitutional democracy in the UK. Looked at in this way the Court’s view becomes an entirely unremarkable one: namely, that untrammelled executive power to prorogue Parliament would render the sovereignty of Parliament a dead letter, with the result that the sovereignty principle must deny the executive any such power in the first place.
A new fundamental principle of accountability and a new approach to conventions?
The Supreme Court thus draws an important inference from what is generally considered to be the kernel of the sovereignty principle — but an inference is entirely warranted. The Court goes on to invoke a second fundamental principle: namely “parliamentary accountability” — that is, the accountability of the executive government to Parliament. Here, the Court refers back to Lord Carnwath’s judgment in the first Miller case, endorsing his view that parliamentary accountability is no less fundamental to the constitution than parliamentary sovereignty. The Court might be thought to be breaking relatively new ground here, by articulating parliamentary accountability in terms of a distinct and equally fundamental constitutional principle. But even if this mode of analysis is novel to some extent, the underlying thinking is surely not. The UK is a parliamentary democracy in which the executive government is not directly elected; rather, it formed out of, is sustained by, and is held to account by Parliament. In such a constitutional setting, to ascribe to the executive government a legally limitless power to neutralise the very institution upon which it depends, and whose constitutional responsibility it is to hold the executive to account, would be nothing other than perverse.
Of course, the notion of executive accountability to Parliament — or ministerial accountability — is generally regarded as a constitutional convention. The question therefore arises whether the Supreme Court in Cherry/Miller (No 2) did something in respect of constitutional conventions that is itself novel and/or which is inconsistent with the conservative stance it adopted in that regard in the first Miller case. In particular, does the Court by invoking accountability in the way that it does, somehow elevate a constitutional convention into a legal principle, thereby doing the very thing that it said courts should not do in Miller (No 1), in which it said that courts were neither the “parents” nor the “guardians” of conventions?
The answer to that question is “no”. The Court in Cherry/Miller (No 2) manifestly does not legally enforce the constitutional convention of executive accountability to Parliament, and therefore does not treat that convention as a legal principle. What the Court does — and it is entirely justified in doing so — is to take legal cognisance of the underlying constitutional reason or principle that underpins and animates the convention of accountability to Parliament. The principle in question is that in a parliamentary democracy, there must be adequate opportunity for the executive government to account to and to be held to account by the legislature. There is no reason why this constitutional principle cannot both underpin a constitutional convention — and thus institutionalise a required mode of political behaviour — while also serving as a constitutional standard to be applied when lawfulness of executive action by reference to the scope of its legal powers. This does not amount not to judicial enforcement of a constitutional convention. Rather, it reflects the reality that the dividing line between the political and legal spheres of the constitution is not rigid, and that fundamental principle can and does inform both conventional practices and legal analysis. Viewed in this way, the legal significance ascribed by the Court in Cherry/Miller (No 2) to the constitutional principle underpinning the convention of accountability to Parliament is wholly unproblematic, and serves as an important reminder that the legal and the political constitutions are related as well as distinct.
A new approach to justiciability?
As noted above, the Divisional Court took the view that the relevant issues were non-justiciable, and that the court could therefore play no part in this matter. In disagreeing with the Divisional Court on this key point, the Supreme Court was careful in the way in which it characterised the nature of the issue before it. Clearing the decks, the Court rightly pointed out that the mere fact that a question before it “is political in tone or context” cannot render the matter non-justiciable. The question is not whether the issue arises in circumstances that are political in nature — if that were the test, then few, if any, government decisions would be amenable to judicial review. Rather, the question is whether the issue amounts to a legal question, whatever political implications that question might have. Having established these basic propositions, the Court concluded that the issue before it was indeed a legal issue and that, as such, the issue could not be non-justiciable, legal questions being par excellence questions for the courts.
How did the Court reach this conclusion? It did so by holding — as I argued, in an earlier post, that it should — that the issue before it concerned not the lawfulness of the exercise of the prorogation power, but the logically and legally prior question of whether, to begin with, there was a relevant and sufficient power capable of being exercised in the first place. This is not to suggest (and the Court was not suggesting) that there is no prorogation power at all: but the crucial issue, according to the Court, was whether the scope of that power had been exceeded. The Court thus drew a distinction between questions about “the lawfulness of the exercise of a prerogative power within its lawful limits” and questions about “the lawful limits of the power and whether they have been exceeded”. This may, at first glance, appear to be a distinction without a difference. However, what the Court appears to be doing is drawing a distinction between judicial review challenges that are concerned with whether the impugned executive action lies with in the scope — or, as it is sometimes put, the “four corners” — of the power, and challenges which contend that a power exercised within its “four corners” has nevertheless been used unlawfully (e.g. on the ground that the rules of natural justice were not observed in its exercise).
In my earlier post on this topic, I argued that if the issue in Cherry/Miller (No 2) were approached in terms of determining whether the power had been used for an improper purpose — such as avoiding accountability to Parliament — then this would render the issue justiciable. I made that argument precisely on the ground that this would go to the question of the scope of the power as distinct from (to use the Supreme Court’s language) the lawfulness of the exercise of the power within its lawful limits, my argument being that (to use the Court of Session’s language) the prorogation prerogative does not in the first place extend to the “stymying” of parliamentary scrutiny of government. The Supreme Court’s approach, however, is different in one important respect from that which I advocated. The Court chose not to address the question of the propriety or otherwise of the purpose for which the power was used, but instead considered the adequacy of the reasons advanced by the government in support of a prorogation decision that impinged upon fundamental constitutional principles. This allowed the Court to avoid potentially fraught questions about the Prime Minister’s motivation in attempting to secure an unusually long prorogation.
A new approach to the standard of review and the principle of legality?
The question arises, however, whether in addressing this problem the Court merely created another. Surely, it might be argued, the question that the Court set for itself — namely, whether there was an adequate reason to support an executive act that impinged upon a fundamental constitutional principle — concerns the lawfulness of the exercise of an acknowledged power, rather than a prior question about the scope of that power? Such a view would seem to follow from the fact that questions about the adequacy of reasons would appear to raise questions about the reasonableness of administrative decisions — questions that are traditionally understood in taxonomical terms to be about the lawfulness of the exercise of administrative powers as distinct from their scope. But if the issue were characterised in this way, doubt would have been cast on the appropriateness of judicial oversight: the court would no longer merely be answering a crisp legal question about the scope of power, but would instead be involving itself in the superintendence of the exercise of the power.
However, the Court avoided any such problem by, in effect, holding that there is no sufficient power in the first place to prorogue Parliament when doing so would interfere with fundamental constitutional principle for no adequate reason. This was achieved by, in effect, treating the relevant constitutional principles — absent reasonable justification for their infraction — as hard limits upon the scope of the power. In other words, the Court (without saying as much) treated the issue as one of ultra vires, the conclusion being that (in the absence of an adequate justification) the government never in the first place had authority to prorogue Parliament contrary to fundamental principles. In this way, questions about the adequacy of the government’s reasons are transformed from matters that would bear upon the reasonableness of the decision to matters that determine whether, to begin with, the scope of the power — in the “four corners” sense — has been exceeded.
This does not break entirely new ground, but it does mark a significant extension of the principle of legality. In El Gizouli  EWHC 60 (Admin), the Divisional Court sought (wrongly, in my view) to confine that principle to an interpretive one that (therefore) applies only to legislation. In Cherry/Miller (No 2) the Supreme Court makes it plain that the principle of legality is a principle of much broader application that can cause prerogative power to be limited by fundamental constitutional principle and which can thus bring about, in effect, the elision of review on reasonableness and scope-of-power grounds, thereby allowing justiciability-based objections — which have traditionally enjoyed particular purchase in respect of prerogative powers — to be neutralised. A potential concern with this approach is that it short-circuits the deferential approach to review that is normally applicable when the unreasonableness doctrine applies, by instead treating the matter as one of vires that is unencumbered by the high Wednesbury threshold. That is, the question is no longer, on this approach, whether the impugned action is manifestly unreasonable, but is rather whether the court is satisfied that the reason offered in support of it is satisfactory. That is, on the face of it, a much more exacting test, and its substitution is open to the potential criticism that by a conceptual sleight of hand, the Court is facilitating a much stricter form of scrutiny.
There are, however, two reasons why this concern is likely misplaced — provided that the courts apply this approach with appropriate sensitivity. First, it is to be inferred from the judgment in this case — as well as from judgments in other cases that have invoked the principle of legality — that this is approach is only available to begin with when a fundamental constitutional principle (or right) is in play. It is this that triggers the limit on vires by dint of denying the executive any authority to interfere with the relevant principle absent adequate justification. The normative case for such heightened scrutiny when basic constitutional principles or rights are at stake is plain.
Second, it would be wrong infer from Cherry/Miller (No 2) that the Court’s approach to the reasonable justification assessment, when enforcing scope-of-power limits derived from constitutional principle, will be uniformly high. Indeed, while this proposition was not significantly tested by the facts of the case, the Court acknowledged it and signalled that it would be sensitive to it where relevant in the future. The reason why the proposition was not significantly tested in this case is thanks to the weakness of the government’s own case. This relieved the Court of any need to closely to evaluate the quality of the government’s reasons for the prorogation: instead, the Court found it “impossible … to conclude, on the evidence that has been put before us, that there was any reason — let alone a good reason — to advise Her Majesty to prorogue for five weeks” (my emphasis).
However, the Court went on to indicate that if relevant reasons had been offered, thus necessitating their qualitative evaluation by the Court, it would have recognised that “the Government must be accorded a great deal of latitude in making decisions of this nature”. The clearly implies that the standard of review of the quality of any reasons would have been relatively deferential bearing in mind the context, which in turn suggests that by applying the principle of legality the Court is not straightforwardly flicking a switch that swaps reasonableness for correctness review: the question remains whether there is reasonable justification, and what will be taken to constitute such justification will vary according to the context. Importantly, however, no occasion for such deference arose in Cherry/Miller (No 2) because, to begin with, no reasons capable of supporting the decision were offered by the government. The proposition that the court will not and cannot defer to the executive in the absence of the executive having taken relevant steps, including by means of considering relevant issues and formulating relevant reasons, is uncontroversial, as the House of Lords acknowledged in Miss Behavin’  UKHL 19.
Conclusion: A new approach to constitutional adjudication or the application of established principles?
So does Cherry/Miller (No 2) break new ground? Does it represent a new approach to constitutional adjudication? Taken in isolation, none of the potentially innovative features of the case identified above is necessarily ground-breaking. From the doctrine of parliamentary sovereignty, the Court draws a sensible and warranted inference. The Court acknowledges that the notion of executive accountability to Parliament is not only (as has long been recognised) something that is institutionalised in convention, but is also a constitutional principle that is capable of informing analysis of the legality of executive action and shaping the parameters of governmental authority. Yet in offering this insight, the Court does not affront the orthodox view that conventions are not legally enforceable. Meanwhile, the Court engages in judicial review in relation to a prerogative power that has never before been subject to review, but in doing so applies established principle, given that the Court is careful to frame its task as one of purely legal analysis. Moreover, the Court acknowledges that if relevant reasons had been advanced by the government, its evaluation of their adequacy would have had to be informed by considerations of due deference, given the latitude that the government properly enjoys in this sphere. And in characterising the specific legal question that falls to be answered, the Court invokes an existing principle — the principle of legality — albeit in a novel way, by applying it to prerogative power.
Nevertheless, while it is possible to present each part of the analysis in the case as at least relatively orthodox, the judgment’s cumulative significance is greater than the sum of these parts, and it undoubtedly represents an important milestone in the narrative arc of modern public law in the UK. Taken in combination, the various factors that are at work in this judgment paint a picture of a Supreme Court judiciary that is prepared to serve as a guardian of constitutional principle in a way and to an extent that previous generations of apex court judges in the UK were not. What stands out about this case is the way in which fundamental constitutional principle is operationalised so as to produce significant and concrete limitations on governmental powers that have hitherto been considered to be no-go areas for the courts. In the principle of legality, the courts have long had at their disposal a powerful tool for confining the executive’s legal capacity to affront fundamental constitutional principle. But in Cherry/Miller (No 2), the potential of that principle is writ large — thanks both to the Supreme Court’s resistance to attempts artificially to limit or marginalise the relevant principles and to the Court’s willingness to apply those principles not only to a prerogative power but to a power that was (incorrectly) considered to lie deep within political territory and thus to be wholly off limits to judicial review.
What, then, are we to make of this case? Is it a legal landmark, or is it an orthodox application of existing constitutional principle? It is both. The judgment affirms, articulates, clarifies, develops and applies fundamental principles governing the place of Parliament within the constitution and its relationship with the executive. In this sense, the judgment is either orthodox or is at least firmly rooted in orthodoxy. What renders the judgment a legal landmark is the willingness of the Court to take those principles to their logical conclusion in the face of a perfect storm of factors that, on the more superficial analysis favoured by the Divisional Court, appeared to close the door to judicial review. Thus the Supreme Court was prepared to draw inferences from, rather than relying exclusively on the formal core of, the principle of parliamentary sovereignty. It was willing to spell out the legal-constitutional implications of the political-constitutional principle of executive accountability to Parliament. It rejected the sloppy argument that because the issue had political implications it could not, at root, be a legal matter. It extended the principle of legality such that it now falls to be understood — as it always should have been — as a mechanism for giving concrete legal effect to fundamental constitutional principle, irrespective of whether the legal powers at stake are conferred by legislation or arise under the prerogative. And — crucially — the Court was prepared to take all of these steps simultaneously, with the result that what appeared, following the Divisional Court’s judgment, to be an utterly hopeless case culminated in a powerfully reasoned and unanimous Supreme Court judgment.
This helps us to understand why the case is capable of being at once both rooted in orthodoxy and path-breaking. The Supreme Court was prepared to take a series of significant — but individually entirely legitimate — legal steps in circumstances that were politically extraordinary and that resulted in the transformation of fundamental principle into hard and novel limits on executive authority. In doing so, the Court does something that is both trail-blazing and mundane. It is trail-blazing because “forbidden” executive territory has been shown to be anything but by a Court prepared to treat fundamental principle as something that is neither a mere rhetorical flourish nor something arid and technical to be understood in isolation from the broader constitutional landscape in which it sits. Yet the judgment is simultaneously mundane because, in the final analysis, it stands for the most modest of constitutional propositions: that the UK is a democracy founded on parliamentary sovereignty, executive accountability, and the subjugation of government to law; that, from those basic constitutional facts of life, it follows that the government is not afforded an unfettered power to deny the legislature the opportunity to perform its vital constitutional role; and that questions about the legal scope of government power are questions of law for courts of law. Once those self-evident propositions are accepted, it becomes clear that judicial intervention in this matter is a realisation of, not an affront to, the separation of powers. Indeed, for the Court to have declined to play its part, and to have refused to determine and enforce the legal limits upon the government’s authority to suspend Parliament, would have been nothing other than a dereliction of its constitutional duty.
I am grateful to Jack Williams for his comments on an earlier draft of this post. The usual disclaimer applies.