Where does law begin and politics end? Any government’s relationship with parliament is bound to be political. Ever since the 18th century, ministers have made use of the power to prorogue or (until 2010) dissolve parliament for political advantage.

There was a consensus that they should not abuse the power, but what amounted to abuse was itself a political question, not a legal one. What is revolutionary about the Supreme Court’s decision is that it makes the courts the ultimate arbiters of what political reasons are good enough.

Yet the Supreme Court’s judgment should be welcomed even by those who believe, as I do, that politics is not the proper business of courts of law. The objection to judicial intervention in politics is that it