‘[A]t some risk of over-simplifying,’ Lord Hughes said in his dissenting judgment in the Miller case, the main question for decision centred on two well-accepted constitutional rules. The first rule, he said, is that the executive government cannot change the law made by Act of Parliament. The second is that the making and unmaking of treaties is within the competence of the government. Lord Hughes pointed out that nobody questioned these principles. The question was which of the two applied to the case at hand.

This was indeed a simplification. For another legal principle was also recognised by the parties, namely that both rules are subject to parliamentary legislation. Thus, a fuller statement of the first rule is that the government cannot change the law made by Act of Parliament unless authorised by Act of Parliament, and a fuller statement of the second rule is that the making and unmaking of treaties is within the competence of the government unless prohibited by Act of Parliament.

Academic commentary following the Divisional Court’s decision in Miller recognised the importance of these two principles and the competing syllogisms that flow from them. But syllogisms always consist of both major and minor premises. Much of the argument and reasoning in the Miller case focussed on the minor premises rather than the question of which of two competing major premises governed the case.

The validity of the minor premises turned on the construction of the European Communities Act and other statutes that give domestic effect to EU rights. Several questions therefore arose, such as whether these Acts give effect to rights of a kind that can only be changed by an Act of Parliament (noting that the rights are created by EU institutions and apply in the UK only because of Britain’s adherence to the EU treaties). It was also considered whether the European Communities Act either positively authorised the government to give notice under Article 50 or else prohibited it from doing so.

The resolution of these questions was essential to the determination of the case. However, the majority judgment went further. For in its reasoning it also effectively rejected the proposition that the second major premise had any application to the case. Its main reason for doing so turned, again, on the European Communities Act. According to the majority’s interpretation, that Act effected an important change in the constitutional fundamentals of the country – not only by identifying the EU treaties and EU institutions as new sources of UK law, but by introducing a new meta-principle that in such circumstances the first principle mentioned above (that the unmaking of treaties is a matter of foreign relations within the competence of the government) is subordinated to the second major principle (that the government cannot change law made by Act of Parliament).

That is a very big inference, difficult to justify by reference to the text, structure and history of the European Communities Act alone. It depends, as the majority acknowledged, on the notion that Britain’s membership of the EU was a constitutionally transforming event, which worked changes not only at the level of the minor premises, but also at the deeper level of the relation between the most basic major premises of British constitutional law.

But alas this reasoning harbours a circularity. Article 50 depends for its meaning and operation on the constitutional requirements of the UK as a member state, but the constitutional requirements of the UK are, on the reasoning of the majority, themselves shaped by content of EU constitutional law. And here it is not enough to say that the Parliament has willed this result by virtue of its decision to enact the European Communities Act. For the question at issue concerns exactly what the Parliament intended by that Act. The circularity remains.

Nicholas Aroney is Professor of Constitutional Law at The University of Queensland.

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