Stephen Tierney: Prorogation and the Courts: A Question of Sovereignty

The request made by the Privy Council that the Queen prorogue Parliament was a clumsy and inappropriate attempt to shorten the time available for parliamentary scrutiny of the Brexit process. That much seems clear from papers submitted to the Court of Session in Cherry. It is therefore no surprise that the Inner House was receptive to the petitioners’ argument that the advice given to Her Majesty violated the conventional purposes for which prorogation ought to be used and was therefore unconstitutional (Cherry, [1]; see also Lord Sumption). Where the court erred was in concluding that the act of prorogation was itself unlawful. The intimate relationship between the prerogative power to prorogue and the supremacy of Parliament precludes such a conclusion. If, as seems correct, a response to this breach of convention is warranted, it is one that can, constitutionally, only come from Parliament itself.

In this blog I argue that the juxtaposition of justiciability/‘high policy’ which is typically used to justify judicial restraint in relation to prerogative powers, as others have observed, is of little help. Although the English Divisional Court in Miller II arrived at a more constitutionally-convincing conclusion than did the Court of Session, the reasoning behind its decision, which is largely based upon this juxtaposition, is incomplete. Instead, to understand the case for judicial restraint – more accurately, the drawing of constitutionally appropriate jurisdictional roles – which the constitution demands, we need to categorise certain prerogative powers (including the prorogation power) as the ‘prerogatives of sovereignty’ which capture the legal dimension of sovereignty within our constitution. These prerogatives of sovereignty are fundamental to the relationship between Crown and Parliament, and to the doctrine of supremacy which flows from it.

The concept of justiciability should in the first place be sharpened by distinguishing the inherent jurisdiction of the common law courts from the boundaries of that jurisdiction. The former contains the authority to police the legal limits of the Crown’s authority. The common law courts have long resisted endeavours by Parliament to curtail this immanent jurisdiction. In this fundamental sense no matter is non-justiciable; the courts assert the right to police the boundaries of their own jurisdiction, a point forcefully made by Lord Drummond Young in Cherry [102]. It is also long settled (Council of Civil Service Unions v Minister for the Civil Service) that the prerogative power is in principle subject to review, as are Orders in Council pursuant to such power (R v Secretary of State for Foreign and Commonwealth Affairs, ex parte Bancoult (No 2)). In this over-arching sense prerogative powers are always justiciable. The courts can articulate the limits of their jurisdiction; there are no black or grey zones of executive power where the rule of law does not run.

That said, our constitution prescribes appropriate jurisdictional limits with which the courts ought to delineate the proper scope of their supervisory function. It is a truism that they cannot strike down statutes enacted by Parliament, nor can they extinguish prerogative powers, although they can adjudicate upon the way in which the latter are exercised. The courts, in light of their inherent jurisdiction have taken on the role, quite properly, of articulating the limits of specific prerogative powers. In recognising that parliamentary supremacy prevails legally and practically over the prerogative there are two areas where they legitimately do so. The first concerns situations where the prerogative has been circumscribed by statute (beginning with the dispensing power as curtailed by the Bill of Rights itself). We see this in a well-established line of cases, e.g. Attorney General v De Keyser’s Royal Hotel Ltd, R v Secretary of State for the Home Department ex parte Fire Brigades Union; R (on the application of Miller and another) (Respondents) v Secretary of State for Exiting the European Union (Appellant) etc. The courts police the prerogative because the Crown in Parliament has, through legislation, warranted their engagement; ergo, if the Crown acts for a purpose that conflicts with parliamentary intention it does so improperly (Padfield v Ministry of Agriculture, Fisheries and Food). The second area where the courts rightfully regulate the exercise of particular prerogative powers is in protecting legal rights recognised by the common law (Miller II [44]); here the inherent authority of the common law courts can challenge the exercise of certain prerogative powers in recognition that Parliament, through the Bill of Rights, recognised the former in the process of curtailing the latter. Certain prerogative powers are directly concerned with relationships between the Crown and individuals, such as the prerogative of mercy or the issuing of passports; the courts correctly police these because they are matters squarely within the area of common law rights; they have also in many ways been circumscribed directly or indirectly by statute.

The prerogative power to prorogue Parliament does not however fall into either of these two categories. It was recognised in Cherry that it has not been circumscribed by statute (per Lord Brodie [68]). Indeed, Parliament itself made this clear in the Fixed Term Parliaments Act 2011(FTPA), s.6(1): ‘This Act does not affect Her Majesty’s power to prorogue Parliament’. It was also recognised in Cherry that the exercise of the prerogative power to prorogue does not implicate common law rights (per Lord Carloway [59]).

In trying to distinguish when it is appropriate to review the exercise of certain prerogative powers in certain situations the courts have tended to fall back upon the rather vague conceptions of ‘political’ or ‘high policy’ matters. This is confusing and unhelpful because, in attempting to understand when a prerogative is used in a political way, it invites the courts to consider the motive behind the exercise of all prerogative powers when in fact, as I will argue, the need for constitutional self-abnegation by the courts is far more fundamental, concerning the nature of certain prerogative powers, not their exercise. It has been correctly pointed out by Paul Craig that the reasons to prorogue may not involve high policy or matters of political importance. Indeed Parliament tends to be prorogued for the routine business of facilitating a new parliamentary session. The decision to prorogue is therefore rarely, and indeed constitutionally ought not to be (hence the current proceedings!), a matter of intense political dispute. It can therefore be argued that there is in the present case no issue of high policy from which the courts ought to recuse themselves.

It is here that we need to eschew the notion of politics and high policy in favour of a far more fundamental constitutional reason for judicial restraint in this case; distinguishing the reasons behind a decision to prorogue from the legal act of prorogation. The act of prorogation is nothing less than the expression of sovereign authority by the Crown in Parliament. It is one of a category of prerogative powers that does so. These include the power to grant Royal Assent to legislation, to form a government, to appoint and dismiss ministers and to dissolve Parliament. These prerogative powers are not concerned with the relationship between the Crown and individuals but rather with the central relationship of governing which gives our constitution its meaning and in which we locate supremacy. It is in recognising the category distinctiveness of these powers (the ‘prerogatives of sovereignty’) that we also see the limits of the judicial role. We are also reminded of these limits by Article 9 of the Bill of Rights which expressly excludes from the purview of the courts the internal workings of Parliament, including speech and debate.

The relationship between the Crown in Parliament as one, unified organ of rule is the political fact that denotes supremacy within the UK constitution. In this conception of supremacy Parliament is not distinct from government. Parliament’s role transformed in the 18th century from being a check upon the Crown to working with it as ‘the key instrument of British government’. As Dicey put it: ‘that… the Crown, the Peers, and the Commons acting together – is absolutely supreme, has never been doubted’. (A.V. Dicey, England’s Case Against Home Rule 1886) This symbiotic and tense relationship of supremacy can only be managed by the institutions that constitute it. Lord Browne-Wilkinson stated in the Fire Brigades Union case: ‘The constitutional history of this country is a history of the prerogative powers of the Crown being made subject to the overriding powers of the democratically elected legislature of the sovereign body. The prerogative powers of the court remain in existence to the extent that Parliament has not expressly or by implication extinguished them.’ As the FTPA makes clear, the power of prorogation has not been extinguished; nor has it been statutorily circumscribed. While as a matter of jurisdiction, courts have a general review function in relation to prerogative powers, ‘prerogatives of sovereignty’ as a category are uninhibited by statute because they are vehicles through which the supremacy of the Crown-in-Parliament functions. Simply because a matter is in principle justiciable, it does not follow that adjudication is always appropriate; courts should not seek to regulate the prerogatives of sovereignty where Parliament has chosen not to do so.

But what of the argument, skilfully put by the petitioners in Cherry, that this relationship of supremacy cannot operate if Parliament is in fact prorogued? Lord Drummond Young was attracted to this contention: ‘The courts cannot subject the actings of the executive to political scrutiny, but they can and should ensure that the body charged with performing that task, Parliament, is able to do so.’ [106] (see also Lord Carloway [29] and [35]).

I submit that if prorogation had been granted in an open-ended way, with no time limit, the relationship between Crown and Parliament would be at risk of a fundamental breakdown, even to the point where we would enter another 1688-89 moment. But this would be the collapse of the constitutional order as we understand it; it could not be remedied by the courts. In any event, this is not where we are. Parliament did sit in the period before prorogation took effect and in this period demonstrated its power in relation to the executive by passing a major statute quickly. In this period it could have sought to constrain the prorogation power as it has constrained the prerogative power to dissolve Parliament (FTPA). Other powers in relation to confidence or even contempt were at its disposal. That it did not pursue these options perhaps reflects a recognition that the period of prorogation, although politically controversial, was subject to a clear time limitation and did not entirely preclude meaningful parliamentary deliberation. The constitutional relationship of supremacy between Crown and Parliament has been strained but it has not been broken.

If the Supreme Court upholds the decision of the Inner House it will be deeply ironic that a Prime Minister who has sought, for political advantage, to rely upon an inherent ‘sovereign’ prerogative power of the Crown-in-Parliament to control its own proceedings will have rendered this power subject to an unprecedented level of judicial control; thereby removing a fundamental pillar of that very sovereignty. The Court however should not take this road. It is for Parliament alone to demarcate its sovereign relationship with the Crown. In due course it may decide to subject the prorogation power to legislative control as it has the dissolution power. This remains to be seen. What is vital is that an abuse of convention does not lead the Supreme Court in a direction that could fundamentally alter the nature of supremacy within the constitution. The oversight role of the courts is vital to ensuring legality within the constitution, but this does not extend to policing the fundamental relationship of supremacy that binds the Crown to Parliament. For the rule of recognition within our constitution to continue to make sense, only the supreme body can determine matters of supreme rule.

I am grateful to Ailsa Henderson, Jeff King, Harshan Kumarasingham, Martin Loughlin, Asanga Welikala and Alison Young for very helpful comments.

Stephen Tierney, Professor of Constitutional Theory, University of Edinburgh. The author serves as Legal Adviser to the House of Lords Constitution Committee. This post is written in a personal capacity.

(Suggested citation: S. Tierney, ‘Prorogation and the Courts: A Question of Sovereignty’, U.K. Const. L. Blog (17th Sept. 2019) (available at