Roger Masterman and Se-shauna Wheatle: Miller/Cherry and Constitutional Principle

In an essay published in Elliott, Varuhas and Wilson Stark (eds), The Unity of Public Law? Doctrinal, Theoretical and Comparative Perspectives, we examined Lord Neuberger’s use of constitutional principle-based reasoning in R (Evans) v Attorney General. In that decision, Lord Neuberger – with whom Lords Kerr and Reed were in agreement – employed the pan-jurisdictional ([51]) values attaching to the concept of the rule of law in order to find that s.53(2) of the Freedom of Information Act 2000 did not permit the Attorney General to exercise the so-called ‘Ministerial veto’ power in circumstances where disclosure had previously been ordered by a judge.

Rule of law-based reasoning was central to Lord Neuberger’s judgment in Evans, to the effective exclusion of parliamentary sovereignty, and to the complete exclusion of separation of powers. In consequence, we wrote:

Though Evans was in one sense very clearly about the interrelationship between Parliament, executive and courts, the virtual absence of explicit discussion of separation of power is illustrative of a decision that – while principle-based in its reliance on the rule of law – is otherwise lacking in its detailed consideration of a (perhaps the) key concept through which constitutional organisation and division can be articulated (p.145).

As Simon Lee has observed – and in stark contrast to the decision in Evans – conceptual analysis of the rule of law is conspicuous through its absence from the Supreme Court’s reasoning in Miller/Cherry. Principle-based reasoning nonetheless provides the foundation for the Court’s judgment, and, as such, Evans stands as an intriguing counterpart – or foil – to the Supreme Court’s more recent decision in Miller/Cherry.

Separation of powers

The Neuberger position in Evans, we suggested, ‘reinforces a trend in British constitutionalism … for a prioritisation of the relationship between the individual and the state’ while being ‘more tepid in addressing the relationship[s] between organs of state (p.140).’ Miller/Cherry, by contrast, explicitly addresses the relations between courts, Parliament and executive. While we noted that Evans paid – aside from in the dissenting judgment of Lord Wilson ([171]) – scant regard to separation of powers, Miller/Cherry addresses more directly this central organisational concept of constitutional law.

First, the Supreme Court in Miller/Cherry conceptualises the judicial function using the language of ‘checks and balances’, regarding the supervisory role over the power of prorogation as a means of ‘ensuring that the Government does not use the power… unlawfully’ ([34]). This specific element of the separation of powers is laid out against the backdrop of a broader point – and one that must have normative purchase, even within the so-called political constitution – relating to the role of the court as arbiter of the law:

It is [the courts’] particular responsibility to determine the legal limits of the powers conferred on each branch of government, and to decide whether any exercise of power has transgressed those limits ([40]).

This particular turn of phrase is reminiscent of Lord Hoffmann’s speech in the ProLife Alliance case – where it was argued that decisions as to the constitutional locus and limits of a particular power were ‘question[s] of law and must therefore be decided by the courts’ ([75]) – and is notable for the Supreme Court’s positioning of this power in relation to ‘each branch of government’ (emphasis added). Determination of the ‘existence’ and ‘legal limits’ of prerogative powers are similarly classified as ‘questions of law’ which ‘[u]nder the separation of powers, it is the function of the courts to determine’ ([36]).

But for the assertive demarcation of the judicial function that is apparent in the above, it is important also to emphasise that the conception of separation of powers advanced by the Supreme Court is not straightforwardly so court-focused. In other words, the Miller/Cherry decision does not advance a conception of power allocation (or of constitutional accountability) that – as at least one prominent critic ([17]) has effectively suggested – simply seeks to extend the reach of judicial power, ‘radically destabilising’ the political realm in the process ([12]). Instead, Miller/Cherry demonstrates a keen awareness of the position and function of the court as a component of a system. First, it illustrates that the constitution’s parallel systems of accountability may influence the intensity of judicial intervention:

The principle of Parliamentary accountability has been invoked time and again throughout the development of our constitutional and administrative law, as a justification for judicial restraint as part of a constitutional separation of powers ([47]).

Second, and more importantly, the Miller/Cherry decision seeks to position the court – and its function – within the constitutional network completed by the executive and legislature. One of the things we suggested was lacking in Evans was an effort by Lord Neuberger to relate his rule of law-driven reasoning to the constitutional framework within which that largely judicially-articulated concept resounded; we described this as a failure to complete the ‘constitutional circle’ (p.144-146). Miller/Cherry is a departure from Lord Neuberger’s approach in Evans for the reason that it explicitly frames the judicial role as operating in parallel to political processes of accountability, simultaneously emphasising the – in this context at least – definitive role of the court as interpreter of law, as well as the limitations of that role in the context of what we might (unsatisfactorily) term questions of political judgment.

Parliamentary sovereignty

While explicit consideration of parliamentary sovereignty was lacking from Lord Neuberger’s judgment in Evans, case-law on parliamentary sovereignty might otherwise be argued to reflect a series of general trends:

(i) the ‘judicially-passive’, recognising Parliament’s constitutionally unfettered ability to enact legislation (for instance, Ellen Street Estates [1934] 1 KB 590, 597; Cheney v Conn [1968] 1 All ER 779, 782);

(ii) the ‘rights-recognising’, allowing (limited) protection to individual rights (via (a) the common law (for example, Witham [1988] QB 575; Simms; UNISON) and (b) the HRA (Ghaidan v Godin-Mendoza); and

(iii) the ‘institutional’, concerning the broader parameters of Parliament’s legislative powers (including, Factortame (No.2); Jackson; Miller).

The cumulative effect of those category (ii) and (iii) cases has been to incrementally map the extent to which primary legislation might interfere with constitutional principles and/or individual rights, as well as interactions between the legislative powers of Parliament and the other institutions of government. In differing ways, each relates to the quantification of Parliament’s sovereign power in accordance with standards which (though often legislatively-derived) are constitutionally expressed by the courts.  

Miller/Cherry is of a slightly different order. As we have outlined above, it stands alongside those decisions that chart the contours of institutional relationships within the constitution. But its conception of sovereignty significantly differs from those decisions which might be seen to quantify the boundaries of primary legislative power. Miller/Cherry is notable because it is facilitative of parliamentary sovereignty; rather than concerning the boundaries of Parliament’s legislative powers, it addresses the conditions under which those powers are exercised. In a sense, it contains echoes of those (in)famous instances in which judges have suggested judicial obedience to statute might not survive an Act designed to significantly abuse or curtail the franchise (for instance, Moohan v Lord Advocate, [35]). Miller/Cherry employs many of the same motivations evident in hypothesising judicial responses to the legislatively ‘unthinkable’ ([1995] PL 57) – namely, the preservation of the parliamentary/democratic process – not in response to an Act of Parliament, but as a rejoinder to an act of the executive carried out under the prerogative.

The structure of structural principles

The Supreme Court’s concern for parliamentary process extends to its substance, and envisages Parliament’s sovereignty as co-existing with the ‘constitutional principle’ of ‘Parliamentary accountability’ ([46]). As such, the Court views parliamentary sovereignty as persisting only in so far as it is underpinned by the principle of parliamentary accountability. For the Court it follows that the latter principle may be frustrated – and the sovereignty of parliament therefore undermined – by way of an ‘unlimited’ power of prorogation ([44]). As to what would amount to an ‘unlawful’ prorogation, the Court says the following:

… 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 a 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 ([50]) (emphasis added).

This passage and the thrust of the judgment can be seen as a further triumph of the culture of justification and the demand for reasoned judgement in public decision-making. Moreover, the Court provides the outline of a bifurcated process for determining whether there has been breach of a constitutional principle; in this case, that requires first assessing whether prorogation has violated the sovereignty principle and then assessing whether there is reasonable justification for the violation. Both the bifurcated process and the reasonable justification standard are hallmarks of adjudication under written constitutions. In particular, the requirement of ‘reasonable justification’ for interference with a constitutional principle approximates the common requirement under modern codified constitutions that rights can only be subject to such limitations as are justified in a democratic society and the proportionality test that is often activated to determine whether limitations are justified. Miller/Cherry in this sense represents a further step in the UK’s march towards modern constitutionalism, represented by both the reassertion of embedded common law doctrine and the adoption of external constitutional elements.

Yet, while the UKSC judgment in UNISON was cited as authority for the reasonable justification standard, UNISON addressed the extent to which the fundamental constitutional right of access to courts – rather than a structural principle – could be contravened by statutory powers. Further, the requirement for justification in UNISON could be partly explained, not only as a sensible interpretation and adoption of precedent on common law rights, but also, on the basis that a similar standard would be applied under Article 6 of the ECHR. The transferability of the UNISON structure to the constitutional principles of parliamentary supremacy and accountability can perhaps be justified on two bases. First is a belief in the core similarities between structural norms and rights, which is that they both operate as principles – that is, they can be fulfilled to varying degrees and do not apply in all or nothing fashion. As such, both constitutional principles and constitutional rights accommodate a balancing exercise to ensure simultaneous respect for competing imperatives within the state. Second, by stating that prorogation would be lawful if reasonable justification is presented, the Court exercises a form of deference to the government. The judges thereby provided space to the government to provide reasons for its interference with parliament’s constitutional duties.

The Court’s outline of the limits on the power of prorogation also highlights the difficulty of reasoning by principle, of finding the specific from the general. Few would deny the centrality of political accountability to the constitution; few would also deny that the democratic credentials of the legislature (and its legislative products) supplement the concept of sovereignty. The frustration of parliamentary sovereignty and accountability provides a general standard, but – in leaving a number of significant questions begging – provides only a partial guide to future governmental (and judicial) activity.


It may be that the core significance of Miller/Cherry is located in its reaffirmation that prerogative power no longer inhabits the ‘dead ground’ of the constitution ([1995] 2 AC 513, 567 (Lord Mustill)). It may be that its findings in relation to the circumstances in which prorogation will be unlawful are confined to the (lamentable) circumstances prompting the litigation. But neither consideration should diminish the significance of the Court’s embrace of principle-based reasoning. Moreover, while we may quibble about which principle – particularly the rule of law or parliamentary sovereignty – is dominant, the Court seems to indicate that these principles hold each other in balance and that their effect depends on the factual context of the case. Thus, the robust articulations of the rule of law found in Evans (and Privacy International) have not usurped the constitutional place of parliamentary sovereignty; Parliament’s constitutional role was the central concern of the 11-strong Miller/Cherry bench. Abstract debates about the supremacy of parliament versus the rule of law are therefore less meaningful – and less predictive. More instructive is the Court’s emerging approach of applying constitutional principles through a structured analysis consistent with the recognition of competing constitutional imperatives.

Roger Masterman and Se-shauna Wheatle, Durham Law School

(Suggested citation: R. Masterman and S. Wheatle, ‘Miller/Cherry and Constitutional Principle’, U.K. Const. L. Blog (14th Oct. 2019) (available at