British law is not all statute; some of it is "common law", which is essentially judge-made caselaw. The prorogation does not contravene statute, and wasn't hel

British law is not all statute; some of it is "common law", which is essentially judge-made caselaw. The prorogation does not contravene statute, and wasn't held to. There is a long line of caselaw going back to the 1600s about the relationship of the Crown to Parliament which have been held to limit executive power, though. The court today held that the constitutional rule limiting royal power works to prevent prorogation under the circumstances seen this year. Although the result is novel, this isn't particularly unusual for how the British legal systems work. Similar in principle to DC v Heller in the US Supreme Court, I suspect: the second amendment is known, but what is means for a particular DC handgun law isn't obvious until SCOTUS rules. The same here: the principle that the Crown can't use the prerogative to frustrate Parliament is now well established (starting with the Case of Proclamations [1610] EWHC KB J22) but it hadn't been tested in court whether that applied to these circumstances. Now we know.