A few months ago, I completed work on a new paper that will appear in an edited collection of essays, soon to be published by Hart Publishing, that examines the constitutional implications of the UK Supreme Court’s judgment in Miller — in which it was held that the process of withdrawing from the EU under Article 50 of the Treaty on European Union could not be triggered by the Government using prerogative power. The effect of the judgment was to put Parliament, as opposed to Ministers, in the driving seat by preventing the withdrawal process from getting underway absent primary legislation authorising the Government to initiate it.

In terms of the politics of Brexit, Miller now looks like something of a damp squib. Parliament was handed by the Supreme Court a golden opportunity to shape the Brexit process, yet that opportunity was squandered. Parliament could, for instance, have legislated to require the Government to submit its negotiating objectives for parliamentary consideration, and could have stipulated that Ministers would be allowed to trigger Article 50 only when — and if — those objectives had secured parliamentary approval. Instead, Parliament blithely enacted the European Union (Notification of Withdrawal) Act 2017, handing the Prime Minister the broadest of discretionary powers to initiate Brexit — which she promptly did, long before her ‘Brexit means Brexit’ mantra had been imbued with any meaningful content. It is precisely because Parliament wasted the opportunity that arose following Miller that it now finds itself scrambling to exercise some degree of control over the Brexit negotiations and to grapple — while the Article 50 clock relentlessly counts down — with basic questions about what sort of future relationship with the EU the Government should be attempting to negotiate.

But for all that Miller did not produce the political consequences that — in the hands of a less supine Parliament — it might have done, its constitutional significance should not be doubted. Indeed, when the legal history of the United Kingdom’s membership of the European Union comes to be written, it is likely to be bookended by two seminal decisions of the UK’s apex court: the judgments of the Appellate Committee of the House of Lords in Factortame and of the Supreme Court in Miller. In my essay, I argue that each case, in its own way, illuminates the British constitution: either by grappling with what it meant in constitutional terms to become a Member State of the EU, or with what that membership has entailed and what the legal and constitutional implications of departure will be. At the heart of each case are questions about the nature and status of EU law with respect to the UK’s domestic legal system. And while Miller is not, in the same way as Factortame, directly concerned with the doctrine of the primacy of EU law, questions about the nature and status of EU law within the UK legal system are nevertheless central to the issues that were at stake in Miller. Yet while the relationship between the notions that Parliament is sovereign and that EU law has supremacy is perhaps the most acute of the constitutional issues raised by membership, the precise nature of that relationship is still far from clear.

I argue in the paper that by introducing the construct of the primacy of EU law into a legal system characterised by the principle of legislative supremacy — thus creating what looks, at least a first glance, like a classic immovable-object-meets-irresistible-force problem — EU membership has forced UK public lawyers to think long and hard about the very nature of the domestic legal order. But just as interesting as the answers that these questions have generated is the way in which the questions have been confronted, including the degree of uncertainty that has been allowed to persist in relation to genuinely fundamental constitutional issues. In this sense, the UK’s involvement with the EU shines a light on the deeply pragmatic nature of the British constitution, whereby fundamental questions are confronted only when, and to the extent, that such confrontation is strictly required. The risk, however, is that such a strong commitment to pragmatism yields — and masks — a degree of theoretical ambivalence that becomes highly problematic when hard questions arise, as they did in Miller.

In my paper, I explore these issues — that is, substantive questions about the accommodation of EU primacy by the domestic constitutional system and broader questions about the way in which these matters have been dealt with — in tandem. In doing so, I pay particular attention to the question of whether this episode in UK constitutional history teaches only specific lessons about how EU law has been accommodated — lessons that may be of little if any relevance when or if the UK fully withdraws from the EU — or lessons of a more enduring kind that will remain pertinent long after withdrawal. I argue that it is lessons of the latter type that can be derived from attempts to understand the relationship that has existed this last half-century or so between the domestic and European legal orders.

However, I argue too that the extraction of those lessons involves a degree of supposition and inference that speaks volumes about the way in which fundamental constitutional questions are (and are not) confronted in the UK. The UK’s European sojourn is thus revealing, but only to a degree, of the substance of the domestic constitution. But to the extent that it is less than revealing, the opacity that we encounter serves not simply to obscure the substance but to illuminate something more visceral: namely, a preference that can be discerned within UK constitutional adjudication, at least when it comes to the very biggest questions, for constructive ambiguity over conceptual clarity.

A pre-publication draft of my paper, ‘Sovereignty, Primacy and the Common Law Constitution: What has EU Membership Taught Us?’, can be downloaded via SSRN. The paper forms a chapter of a collection of essays on the Miller case: Mark Elliott, Jack Williams and Alison L Young (eds),The UK Constitution After Miller: Brexit and Beyond(Hart Publishing, 2018).