In my July 4 post on Brexit, I wrote:
… to put the EU question directly to the voters flies in the face of what I thought I knew about the UK constitution, particularly the idea of Parliamentary sovereignty. Some of the legal reaction to Brexit seems to bear this out. Assuming for the moment that the decision to invoke Article 50 of the EU Treaty isn’t a matter within the prerogative powers (if it were, the decision would be for the government), doesn’t Parliament still need to vote?
As it turns out, this was the right question to ask, and the assumption I made—that invocation of Article 50 wasn’t within the government’s prerogative powers—was correct, though contested.
In today’s case of the day, R. ex rel. Miller v. Secretary of State for Exiting the European Union,  EWHC 2768 (Admin), the High Court held that in fact invocation of Article 50 is not within the prerogative power. The basic reasoning is that the prerogative power cannot be used to override statutes enacted by Parliament. Since, the EU treaty is not self-executing in UK law, Parliament enacted statutes to give effect to the treaty. So while the government has the prerogative power to enter into treaties, once Parliament has legislated so as to make treaties effective and to create rights that withdrawal from the treaty would destroy (for example, the right of freedom of movement within the EU), only Parliament can repeal the implementing legislation. (Well, it’s a little more complicated than this—read the opinion!)
The furious reaction to the decision is a little hard to understand in principle, though as a raw political matter I suppose it makes sense. The Brexit campaigners wanted to restore Parliamentary sovereignty and the supremacy of British law as the law of the land. Isn’t that what they’re getting in this decision? On the other hand, the outcome of the referendum was clear, and so Parliament will no doubt face a real political firestorm if it uses the decision as an excuse to ignore the popular will as expressed in the referendum.
The High Court’s decision may not be the last word, as the government has promised an appeal to the UK Supreme Court. Stay tuned.