Understanding what makes “Miller & Cherry” the most significant judicial statement on the constitution in over 200 years

The Supreme Court decided in Miller & Cherry that parliament was not prorogued, since the prime minister’s advice to the Queen was unlawful. The temptation is to dissolve the case into Brexit politics. Brexit, combined with parliamentary arithmetic and the Fixed-term Parliaments Act, produced the circumstances that triggered the case, a rupture between government and parliament that is rare within our system. Brexit also brings sharpness and intensity to questions about our political life. But seeing the case solely through this lens misses its real character. Only by attending to the patterns of continuity and innovation that it traces can we understand what makes it quite possibly the most significant judicial statement on the constitution in over 200 years.

It is hard to think of a more important separation of powers case. Its significance derives from its exposition of the relationship, often blurred, between government and parliament. The case reaffirms the idea of government ministers, including the prime minister, as office-holders within the constitution, with duties corresponding to the magnitude of their office. It strengthens the claim that it is the “particular responsibility” of the court to determine where the legal powers of each branch of government begins and ends.

The fact that Miller & Cherry was a unanimous judgment surprised commentators. It is common to see a number of separate opinions, especially in a case like this where even bringing it broke new ground. A streamlined judgment of only 24 pages, it proceeds without unnecessary complication or ornament. It is as though the Court wanted to show in the process of giving judgment two themes that do so much to shape it—the demands of reason and the constraints of office.

The first issue for the Court was whether prorogation is justiciable—that is, whether the prorogation is reviewable at all by the courts. This was the issue on which the Court spent most time, ultimately deciding “yes.” Many previously considered prorogation a political matter—one of a handful of prerogative powers to which the normal rules of judicial review do not apply. It was thought that this subset continued to operate according to the old law relating to all prerogatives. The court could determine whether a prerogative power existed and had been exercised within its limits; it could not review the way it was exercised. But this is a dynamic area of law. The direction of travel has been to make review of the executive’s prerogative powers as consistent as possible with review of the executive’s statutory powers. The issue of justiciability is increasingly avoided, as judicial concern about how it immunises certain executive powers from legal oversight has increased.

Miller & Cherry is consistent with this trend but gives it an important twist. Prorogation is not immune from judicial review, it decided. Its exercise is unlawful if it “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.” The Court understood that test as “a standard which determines the limits of the power,” rather than a review of how the power is exercised. Whether that distinction is persuasive may be beside the point. The old distinction between review for the existence of prerogative and on the exercise of prerogative collapses once the idea of non-justiciability is jettisoned—a message conveyed pretty clearly in the statement that “every prerogative power has its limits, and it is the function of the court to determine, when necessary, where they lie.”

What animated this outcome—the constitutionalisation of prerogative—is more interesting than doctrinal minutiae. The Court invoked two fundamental constitutional principles: parliamentary sovereignty and parliamentary accountability (the responsibility of government ministers to parliament). Both are essential bedrock principles of our constitution. But there is innovation in the deployment of each.

Parliamentary sovereignty is a longstanding legal principle—indeed, the most important in our public law. Historically it referred specifically to the legislation enacted by the Crown in Parliament. Miller & Cherry extends the term so as to include ancillary functions necessary for the realisation of parliament’s legislative function. This is a significant development—but in my view a justified one, for the reason the Court gave. “The sovereignty of parliament would, however, 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.”

Parliamentary accountability is not so well grounded in public law. Usually it has been introduced by courts as a means of justifying judicial restraint. Its elevation here as a fundamental constitutional principle is consistent with the concern to close gaps within our democratic structures, a specific response to the fear that prorogation might be used to circumvent ministerial accountability until such point as “the government’s purpose in having parliament prorogued might have been accomplished.” More than any other feature, this element reveals the judgment’s basic architecture, which is to restate the constitutive elements of our political (parliamentary) constitution, with additional juridical specification. That granted, the courts now have much work to do in refining the principle, and identifying limits to its operation.

The elaboration of principle meant that by the time the Court turned to the second issue—was this prorogation lawful?—the heavy lifting had been done. Did the prime minister’s action have the effect of frustrating or preventing parliament from holding the government to account? The answer: yes, “of course it did.” Given that effect, could a reasonable justification be identified for the action? Here the unusual length of this prorogation came into play, as did former prime minister John Major’s evidence that no government had needed this amount of time to compile a legislative agenda (the government’s ostensible reason). The current prime minister’s suggestion that the September sitting of parliament was a “rigmarole” seemed to seal the conclusion that no reasonable justification had been given.

That left the question of remedies—what could the court grant the successful claimants? A declaration of the unlawfulness of the prorogation advice was unproblematic. But there had been argument that the Supreme Court was prevented from also deciding whether in fact parliament had been prorogued by Article 9 of the Bill of Rights 1688 which stops “proceedings in parliament” being questioned in court. The Court rightly dismissed that argument on the basis that prorogation, a unilateral act of the executive, is not a “proceeding in parliament.” It is not something upon which MPs can speak or vote, but “something which is imposed upon them from outside.”

Miller & Cherry is a case that will be discussed centuries from now. It is considerably more innovative, and more significant, than the first Miller case of 2017, in which the same court decided that the government could not use its foreign affairs prerogative to give notice of the UK’s withdrawal from the EU but needed first to obtain an Act of Parliament. It clearly has political elements—though not necessarily the ones driving much of the immediate discussion about the case. Chief among these is the explication of the logic of office-holding within a parliamentary democracy. The animating pulse is not Brexit, at least not in any direct or immediate sense. It is the desire, newly urgent, to restate and reinforce the institutional structures which, though continuously evolving, have long sustained our political life. It is not courts who ultimately determine the course of political history. But, as the rain thundered down on Parliament Square, the Supreme Court did what it could to weatherproof the constitution against political storms to come.