In a paper forthcoming in Public Law, I argue for a different understanding of the relationship between UK law and EU law than the one adopted by the Supreme Court in the Miller judgment. On the view I defend, Parliament chose to give effect to EU law in the UK conditionally on the UK’s membership in the EU, which was both to be brought about and potentially to be cancelled by prerogative action of the executive. In other words, there was no legal requirement of an Act of Parliament authorising withdrawal from the EU on the plane of international law.

Firstly, I point to the weaknesses of the Supreme Court’s treatment of the fact that EU (then EEC) law only started to have effect in the UK after the UK entered the European Communities. That is, after the executive, acting under prerogative powers, brought about the UK’s membership in the European Communities on the international plane. Given the domestic effect of the UK’s international obligations provided for by Parliament in the European Communities Act 1972 (the ‘Act’), the executive action of joining the European structures was at least as constitutionally significant as will be Brexit. And yet, it is far from clear that Parliament gave the sort of statutory authorisation to joining (in express terms) that the Supreme Court required from Brexit in Miller. The main point the Miller majority made to dismiss these concerns is that they thought it ‘most improbable’ that Parliament intended to leave domestic effect of European law conditional on ministers not taking the UK out of the European Treaties.

I suggest that this is only improbable on an anachronistic interpretation of the legislative choice made by Parliament in 1972; reading it as if it was enacted in 2016, with a baggage of over forty years of domestic influence of European law. To illustrate: in 1972, it was not at all odd that the ministers withdrew the UK from the European Free Trade Agreement without statutory authorisation.

Secondly, I make an argument from statutory interpretation of the European Communities Act 1972, which did not receive much attention from the Supreme Court and which strongly suggests that the Court misread the statute. My argument focuses on the significance of s. 1(3) of the 1972 Act. Simplifying, this provision requires that both Houses of Parliament approve by resolutions (but not by an Act of Parliament) some future European treaties before those treaties become directly effective in UK law.

Legislative history shows that this provision was included because of a belief that, without it, other provisions of the statute (especially sections 1(2) and 2(1) of the Act) would have provided for automatic direct effect of such future amending treaties, without a binding requirement of parliamentary approval, once entered into by UK ministers on the international plane. Importantly, the amending (‘ancillary’) treaties were thought to include major changes to the relationship between the UK and the EEC/EU. This belief contradicts the Miller claim that an Act of Parliament would have been required to authorise executive action due to cause significant changes in the UK-EU relationship.

Those who worked on the 1972 Act in Parliament would have been surprised to hear what follows from the Miller judgment: that what they achieved was in fact making it easier to incorporate some major amending treaties (by requiring resolutions of the two Houses, instead of an Act of Parliament). There can be little doubt that the intention behind s. 1(3) of the Act was to give decisive voice to the two Houses of Parliament when there otherwise would have been none (in particular, no legal requirement of an Act of Parliament). At the same time, the 1972 Act itself did not go further in ‘protecting’ Parliament, in particular by requiring an Act of Parliament to authorise any executive action on the international plane.

Mikołaj Barczentewicz is a DPhil candidate in the Faculty of Law, University of Oxford.