Brexit, Miller, and the Regulation of Treaty Withdrawal: One Step Forward, Two Steps Back?

In “the constitutional case of the century,” the U.K. Supreme Court concluded that the Government did not possess the prerogative power to withdraw from the European Union. However, while it may be clear from the decision that legislation was required to empower the Government to notify the European Union of its intention to leave, the scope of the Court's reasoning in Miller is otherwise uncertain. At its broadest, the decision would apply to the withdrawal from any treaty that had created rights for individuals, regardless of whether such a treaty had been implemented into domestic law or not. At its narrowest, it only applies to the EU Treaties, which created a set of arrangements in international law that are so esoteric, they are unique to the European Union. To demonstrate how one judgment can generate such a range of interpretations, this essay unravels the different strands of argument running through the decision and considers the criticisms leveled by scholars. It will argue that whether U.K. law requires legislation to withdraw from a treaty depends upon the extent to which that treaty creates rights in domestic law, the constitutional importance of the legislation incorporating the treaty into U.K. law, and the circumstances in which a legal challenge to the use of the prerogative arises. Miller provides no general answer, merely a series of questions.