> Once the courts venture into the political sphere and begin passing judgment on Parliament’s actions, legal analysts say, there is no going back.
The court explicitly did not pass judgement on an action of Parliament.
From page 3 of the summary (https://www.supremecourt.uk/cases/docs/uksc-2019-0192-summar...)
> But it is quite clear that the prorogation is not a proceeding in Parliament. It takes place in the House of Lords chamber in the presence of members of both Houses, but it is not their decision. It is something which has been imposed upon them from outside. It is not something on which members can speak or vote. It is not the core or essential business of Parliament which the Bill of Rights protects. Quite the reverse: it brings that core or essential business to an end.
Instead it passed judgement on an action of the government which it has done for centuries.
From page 2 of the summary:
> The first question is whether the lawfulness of the Prime Minister’s advice to Her Majesty is justiciable. This Court holds that it is. The courts have exercised a supervisory jurisdiction over the lawfulness of acts of the Government for centuries. As long ago as 1611, the court held that “the King [who was then the government] hath no prerogative but that which the law of the land allows him”.