In a forthcoming article in Public Law, Nicholas Kilford and I examine three leading UK Supreme Court decisions that have subjected the principle of parliamentary sovereignty to notably unorthodox treatments. In the face of what can only be described as thin judicial reasoning, we ask whether the Court’s omission can be remedied by constructing an analytical framework capable of making sense of this case law – and ask what these cases tell us about the Court’s deeper vision of the UK constitution.
By Mark Elliott and Nicholas Kilford
Parliamentary sovereignty is perhaps the most important principle in UK constitutional law. However, in three of the most significant constitutional cases decided in the last decade, the UK Supreme Court’s treatment of parliamentary sovereignty has been distinguished by two characteristics – namely, the novelty of its approach to the principle and a paucity of accompanying judicial reasoning. The cases in question are R (Privacy International) v Investigatory Powers Tribunal [2019] UKSC 22, R (Miller) v Prime Minister [2019] UKSC 41 (“Miller II”) and In re United Nations Convention on the Rights of the Child (Incorporation) (Scotland) Bill [2021] UKSC 42 (“UNCRC”).
Against that background, in an article to be published in Public Law, we subject those cases to close analysis. We explore how the Court conceptualises parliamentary sovereignty in them, and pay particular attention to the ways in which the Court appears to understand the relationship between parliamentary sovereignty and other constitutional principles. We identify three ways in which the cases arguably conceive of that relationship, extrapolating from the case law three models that can be used to characterise modes of interaction between parliamentary sovereignty and other principles. Rather than seeing these cases as isolated or insulated accounts of parliamentary sovereignty, confined to their idiosyncratic contexts, we set out this framework in order to explore the extent to which the treatment of parliamentary sovereignty in the Supreme Court might reflect a set of deeper constitutional visions.
Three models
The associative model, we argue, can be discerned in Lord Carnwath’s analysis in Privacy International. On this view, our understanding of a given principle is informed in part by the view afforded of it by a lens supplied by other principles. In Privacy International, for instance, Lord Carnwath arguably viewed parliamentary sovereignty through a lens supplied by the rule of law, leading him to conclude that there may be limits to Parliament’s capacity to exclude judicial review via ouster clauses. The associative model, then, sees constitutional principles as sitting in relationship with one another, our understanding of each individual principle being informed, in part, by how it relates to its counterparts.
That contrasts with the acquisitive model, which we argue is implicit in the judgments of Lord Sumption and Lord Lloyd-Jones in Privacy International. It embraces the possibility of norms traditionally associated with one principle being “acquired”, or annexed, by another principle. Hence, for instance, parliamentary sovereignty might turn out to incorporate – and be limited by – a rule-of-law requirement that insists upon independent courts’ role in interpreting legislation.
A further possibility is supplied by the generative model, which acknowledges the possibility of constitutional principles interacting in ways that give rise to something new. We consider whether Miller II can be understood in this way, with the principles of parliamentary sovereignty and parliamentary accountability combining to generate a new (legally enforceable) principle of parliamentary efficacy – a principle that was offended by a prolonged and unjustified prorogation. The UNCRC case, in which the Supreme Court held that the Scottish Parliament’s power was limited by the UK Parliament’s “unqualified legislative power”, might seem susceptible to comparable explanation, given its embrace of a novel “unqualified power” principle. However, we argue that UNCRC is ultimately difficult to characterise in that way – or, indeed, in any way that reflects a sufficiently coherent analysis of relevant constitutional principles.
Three visions
The three models we develop seek to provide frameworks for understanding what the Court is doing at a practical or mechanical level. However, we also argue that, at a deeper level, these cases – and the various judgments in them – can be read as revealing three distinct visions of the constitution and of the place within it of parliamentary sovereignty. On one view, parliamentary sovereignty is postulated in absolutist terms: a steamroller that flattens all before it, the sovereignty principle necessarily overpowers other principles, which must yield in the face of conflict. On this view, parliamentary sovereignty occupies such a central place within our understanding of the constitution that other constitutional principles risk being overlooked, neglected or hollowed out. We ultimately conclude that this sovereignty as predominant vision of the constitution is so reductive as to be unsustainable.
A second constitutional vision immanent in aspects of the relevant judgments postulates sovereignty as a threat to other principles. Such thinking lends itself to the development of devices capable of taming parliamentary sovereignty – for instance, removing its sharper edges by treating it as incorporating or as having to be understood from the perspective of other principles. This account, we argue, is reductive in a different way: it conceives of the normative constitutional order in atomistic terms, such that its constituent elements ultimately form threats to and sit in an antagonistic relationship with one another.
We conclude the article by arguing in favour of a third vision, which, we contend, can be discerned in some of the judgments on which the article focuses. On the network view of parliamentary sovereignty, the principle sits in connection with other principles as part of a normative network. We suggest that the network view offers the most promising way of making sense of at least some of the case law – and, perhaps more importantly, that it offers a means by which the courts’ jurisprudence in this area might develop in a cohesive manner. This approach involves acknowledging the complex and subtle nature of the web of constitutional principles that sit in relationship with one another, overlapping and often advancing complementary commitments, such that any attempt to characterise such principles’ relationship in exclusively – or even principally – antithetical or adversarial terms is liable to mislead.
There is a risk (which we think is real) that the courts’ recent jurisprudence on parliamentary sovereignty tips over into a bald instrumentalism that treats sovereignty as a blank canvas on which to conveniently project competing, but ultimately unsatisfactory, visions of the constitutional order. The network view – by accounting, we contend, in more authentic terms for parliamentary sovereignty’s place within, and interaction with, the wider constitution – offers a way to ameliorate that risk, supplying instead a principled framework for judicial decision-making. In particular, the network view rejects the reductivism of zero-sum analysis; it requires in its place judicial engagement with the deep, subtle and complex questions that necessarily arise in this area, thereby placing an appropriately weighty justificatory and explanatory burden on the courts when they address questions of fundamental constitutional principle.
A pre-publication version of Mark Elliott and Nicholas Kilford, “The relational principle of parliamentary sovereignty” (forthcoming, Public Law, 2026) can be downloaded via SSRN.
