George Letsas: Non-Justiciability of Prorogation: A Matter of Law and Logic?

The case of Gina Miller v the Prime Minister and Others (‘Miller 2’) is presently being heard by the Supreme Court and the issue of justiciability is central. Some commentators have sought to defend the claimant’s submission that no exercise of a prerogative power is completely immune from judicial review. But the Supreme Court, like the Divisional Court, may not be ready to accept that this general proposition accurately reflects the current state of the law. In this post, I put forward an interpretation that salvages the general doctrine of non-justiciability, while departing from the conclusion that the High Court reached. Even if the Supreme Court is minded to accept the traditional doctrine of non-justiciability, it would still not follow that the specific prorogation before the Court is non-justiciable.

Justiciability as a threshold issue

The High Court treated justiciability as a threshold issue: if prorogation, as a subject-matter of executive action, meets the criteria of the doctrine of non-justiciability, then Government may prorogue Parliament without courts scrutinizing the legality of the reasons for which the executive acted. “The question of justiciability comes first”, the High Court said, ‘both as a matter of logic and of law’. Two things follow from this construction: first, the specific reasons for which Government sought to prorogue Parliament in the case at hand are irrelevant to the question of whether the relevant prerogative power is justiciable. Understood as a threshold question, what matters to justiciability is how the subject-matter of a prerogative power is described in the abstract: does it involve either (a) matters of high policy or (b) political considerations for which there is no applicable legal standard?

Second, if a prerogative power is judged non-justiciable, then it can be exercised by the Executive for whatever reason without the courts assessing its legality. As the High Court put it: “even if the prorogation under consideration in the present case was, as the claimant and the interveners contend, designed to advance the Government’s political agenda regarding withdrawal from the European Union rather than preparations for the Queen’s Speech, that is not territory in which a court can enter with judicial review”. In other words, a ruling of non-justiciability is sweeping: it eclipses from judicial review all the reasons – however noble or improper – for which the Executive acted.

Following the above construction, the Divisional Court interpreted the prerogative power at issue in general terms, as the power to prorogue Parliament for a given number of days. It then examined whether the considerations that are relevant to how long Parliament should be prorogued are political or legal in nature. It found that there is a number of ordinary reasons for which Government may decide to prorogue Parliament, all of which are purely political.

The problem of specification

Judged in the abstract, it is true that the decision to prorogue Parliament normally turns on a number of political considerations (e.g. preparing for a Queen’s Speech, allowing MPs to participate in party conferences etc) for which there is no right legal answer. Or, as we might put it more accurately, the law gives the Executive discretion to balance the pertinent political considerations. But suppose we specify the prerogative power that is at issue in Miller 2 more narrowly. Suppose we specify it as the power of the Executive to escape a statutory constraint that Parliament seeks to impose on it, by suspending Parliament’s constitutional power to legislate. This way of specifying the relevant prerogative power proceeds from the facts of the case at hand. It takes the claimant’s submission as to what the Executive is seeking to achieve, as specifying what the prerogative power under consideration is. Once the power is specified in this way, we can ask whether the exercise of that prerogative power is justiciable.

Here, it is crucial to note that the narrowly specified power of the Executive to escape an impending statutory constraint is different to the general power to balance political considerations that affect the timing and length of prorogation. That the Executive may legally have the latter power does not entail that it has the former. Consider here an analogy with legal rights: that individuals have a general free speech right to decide if and when to speak, and what to say, does not entail that they have a legal right to say, refuse to give a witness statement at the order of a criminal court. (I am grateful to Nicos Stavropoulos for suggesting this analogy.) Imagine a hypothetical law that bans spouses from giving each other the ‘silent treatment’, and a subsequent legal challenge launched under art 10 of the ECHR (freedom of expression). In seeking to justify why that law would violate freedom of expression, courts might say that it is not the law’s business to inquire into the reasons why individuals decide to speak or remain silent to their spouses. These are personal reasons, they might say, which are not reviewable because there is no applicable legal or judicial standard. But when considering the different question of whether individuals have the legal right to refuse to give a witness statement, this justification would not at all pertinent. By ordering a witness to give a statement, a court is not balancing that person’s personal reasons for speaking. Rather, it is giving effect to a legal principle that individuals have a duty to assist state authorities in prosecuting crime.

Just like the specification of a free speech right is crucial with respect its legality, likewise, the specification of a prerogative power is crucial with respect to its justiciability. But specification cannot happen in the abstract. It is only by looking at the facts of Miller 2 that we can surmise that the power at issue is not the general power to decide how many days Parliament should be prorogued, but rather the different power to frustrate Parliament’s legislative function.

Why specification matters

It matters crucially to the issue of justiciability whether the relevant prerogative power is specified in the abstract, as the power to decide various pertinent political considerations about the timing and length of prorogation, or whether it is specified proceeding from the facts of the case. The reason is simple: since they are not the same powers, the former may be non-justiciable, while the latter is. The Divisional Court’s approach however, which treated justiciability as a threshold issue, precluded it from examining whether the latter power is justiciable. It inferred the non-justiciability of the latter power from that of the former. This is analogous to saying that just because there is a free speech right to decide if and when to speak to one’s spouse, there is also a right to decide if and when to give a statement before a court about a crime one has witnessed. The High Court seems to have been led to this approach by the thought that, if it were to examine the facts of the case first and leave the question of justiciability last, it would do away with the doctrine of non-justiciability altogether. This however does not follow. To see this, consider the development of English law since CCSU in other areas of the Royal Prerogative.

Lord Roskill’s list of ‘excluded categories’ in CCSU mentions powers described in the abstract (e.g. the making of treaties, the appointment of ministers etc). In several subsequent cases, courts found the specific exercise of some these abstract prerogative powers justiciable. The case of Youssef v Secretary of State for Foreign and Commonwealth Affairs, involved the decision of the Secretary of State, as a member of the UN Sanctions Committee, to place the claimant on a list of persons associated with a terrorist group. The Supreme Court held that the relevant decision of the Secretary of State was reviewable. One way to describe Youssef is as chipping away at the non-justiciability of the Government’s prerogative power to conduct foreign policy: what was thought to be non-justiciable when CCSU was decided, no longer is. But this would be misleading. The Government’s general power to conduct foreign policy, in the sense of the discretion to balance political considerations for and against voting in particular ways within the UN, remained non-justiciable. By analogy, suppose that the Supreme Court finds in Miller 2 that the power of the Prime Minister to use prorogation in order to frustrate Parliament’s legislative function is justiciable. It would not follow that courts may now review the ordinary political reasons for which Government may choose to prorogue Parliament. That power to prorogue would remain non-justiciable: courts would still be barred from reviewing say, how many days a Government needs in order to prepare a Queen’s speech.

Are all prerogative powers potentially justiciable?

The doctrine of non-justiciability is, by its very nature, confusing. A court has to have some idea of what the relevant power is before it chooses not to review it. But it is not possible accurately to describe a power unless one reviews the reasons for which it was exercised. To that degree, there is no such thing as a non-reviewable power. And the more abstractly a given prerogative power is specified, the more implausible it is that it is non-justiciable. A real or hypothetical case will immediately put pressure on an absolute bar to the justiciability of any prerogative power, generally described. Take the Government’s power to appoint ministers. Courts will not review whether a particular ministerial appointment meets some legal test of merit. The suitability of an appointee is not a justiciable issue. But what if a minister is sacked on account of their race or sexual orientation? Wouldn’t that decision be justiciable? Contrariwise, the more narrowly a given prerogative power is specified, the more plausible the doctrine of non-justiciability becomes. The power of the Prime Minister to decide who has the skills, qualifications, or political influence to serve as a minister is – unlike the power to disadvantage ministers on the basis of their race or sexual orientation – non-justiciable.

The development of English law since CCSU can be characterized as a process of determining which specific prerogative powers – narrowly specified by reference to the facts of a given case – are justiciable and which aren’t. Contrary to what the reasoning of the High Court might suggest, a case by case individuation of the prerogative power salvages, rather than collapses, the doctrine of non-justiciability. If, like Lord Roskill’s list in CCSU, we define royal prerogative powers in abstract terms, then we treat them as rebuttable presumptions: any recognized exception will make the entire prerogative power, defined by its subject-matter, justiciable. By contrast, a case by case process of specification allows us to draw principled distinctions between justiciable and non-justiciable prerogative powers within the same subject-matter. The doctrine of non-justiciability need not evaporate when courts examine it after they inquire into the facts of the case and the reasons for which the Executive acted. There is no error of law or logic when they do so.


Courts cannot examine the justiciability of a given prerogative power unless they specify it first. How a power is specified affects possible judicial outcomes. Specifying the prerogative power in the abstract, without reference to the specific facts of the case at hand, might mislead a court into assessing the justiciability of a power other than the one that is relevant to the case at hand. Understood as the power to decide the timing and length of Prorogation on the basis of a number of ordinary political considerations, it is arguably sound to find the matter non-justiciable. But understood as the Executive’s power to suspend Parliament’s legislative function with a view to avoid a statutory constraint that Parliament wishes to impose on it, then the legal question of justiciability is different. The traditional argument that it is for the Executive to balance the ordinary political considerations with respect to prorogation no longer has relevance. Since the prerogative power at issue in Miller 2 is a new one, a new legal argument for or against its justiciability is needed. It is an argument that the Supreme Court will hopefully address, as a matter of both law and logic.

I am grateful to Stuart Lakin, Virginia Mantouvalou and Nicos Stavropoulos for very helpful comments and discussion.

George Letsas is the Co-Director of the UCL Institute for Human Rights and Professor of the Philosophy of Law at University College London.

(Suggested citation: G. Letsas, ‘Non-Justiciability of Prorogation: A Matter of Law and Logic?’, U.K. Const. L. Blog (19th Sept. 2019) (available at