This may be one of the most significant constitutional law judgments for a generation. In particular, there are four striking qualities to the Supreme Court's decision, writes David Allen Green, FT contributing editor and a lawyer.
First, it does not shy away from setting out starkly the respective roles of the judiciary, the executive and the legislature. It does not hide behind narrow legal technicalities. Many paragraphs are quotable, and they will be quoted in cases and books for many years. The court has knowingly set out the UK's core constitutional arrangements in as accessible a form as possible.
Second, the judgment shows how the court grappled with a complex legal problem so as to set out a new constitutional rule. The rule is: "a decision to prorogue Parliament (or to advise the monarch to prorogue Parliament) will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive." This has been fashioned not from any direct precedent, as there is no direct precedent, but from a careful analysis of other constitutional cases. It is a superb piece of practical jurisprudence.
Third, it is unanimous. Nobody expected this. This means that it has the greatest possible authority as a judgment and makes it difficult to attack as a politicised judgment. The supreme court has fulfilled its constitutional role with every judge onside.
And fourth, and wisely, the supreme court has only made a declaration of unlawfulness. They have not made any other order, like an injunction. They are instead returning the matter to the realm of politics, for parliament and the government to sort out. The judges' job, for now, has been done.
