“The fact that a statute says nothing about a particular topic can rarely, if ever, justify inferring a fundamental change in the law.” Those are the words of the majority of Supreme Court justices in today’s Miller judgment (at paragraph 108). Yet they have done exactly that, by reading in to the European Communities Act 1972 a limitation on prerogative powers about which that statute says nothing. The majority’s judgment is a bad and confused one.

The court claims to be upholding fundamental principle: but which principle? At times, the majority seems to rely on the rule in the Case of Proclamations, that the prerogative cannot change the law; at other times it says only that ministers cannot make a fundamental constitutional change by prerogative. Which is it?

The idea that there are “constitutional statutes” seems to play little role in the court’s reasoning, but the equally novel and fashionable “principle of legality” certainly influences it. This dangerous doctrine (dangerous because it gives judges free-floating power to limit and reject both executive and legislative action, beyond the power given them by EU and human rights law) features at paragraph 87 of the judgment, and, crucially, is inverted. What began as a principle that Parliament could not abridge common law principles except by clear words has become, in the hands of the High Court and now the Supreme Court, a rule that Parliament does abridge common law powers unless it clearly disavows that intention. The principle of legality, supposedly a plank of an emerging “controlled” constitution, is itself out of control.

The good news is that Miller may be confined to its own facts. The European Communities Act 1972 is unique, the majority says, because it provides for EU law to have direct effect. Withdrawing from the EU is unique. It’s that and only that that is now impossible by prerogative, it seems. If the justices really mean that, then at least Miller will not disturb the constitution in any wider sense. But will a future Supreme Court really keep its precedent within such limits?

Carl Gardner is a former government lawyer and current writer at Head of Legal.

Click here for further analysis of the Supreme Court’s Miller judgment.