From the UK Supreme Court's summary of today's hearing on prorogation of Parliament:
The next and final question, therefore, is what the legal effect of that finding is and therefore what remedies the Court should grant. The Court can certainly declare that the advice was unlawful. The Inner House went further and declared that any prorogation resulting from it was null and of no effect. The Government argues that the Inner House could not do that because the prorogation was a “proceeding in Parliament” which, under the Bill of Rights of 1688 cannot be impugned or questioned in any court. 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.
This Court has already concluded that the Prime Minister’s advice to Her Majesty was unlawful, void and of no effect. This means that the Order in Council to which it led was also unlawful, void and of no effect and should be quashed. This means that when the Royal Commissioners walked into the House of Lords it was as if they walked in with a blank sheet of paper. The prorogation was also void and of no effect. Parliament has not been prorogued. This is the unanimous judgment of all 11 Justices.
It is for Parliament, and in particular the Speaker and the Lord Speaker to decide what to do next. Unless there is some Parliamentary rule of which we are unaware, they can take immediate steps to enable each House to meet as soon as possible. It is not clear to us that any step is needed from the Prime Minister, but if it is, the court is pleased that his counsel have told the court that he will take all necessary steps to comply with the terms of any declaration made by this court.
If I am understanding this correctly, the court not only ruled in favor of the UK Parliament, but also stripped the UK government of its ability of proroguing Parliament against its will in the future -- nullifying the PM's claim that they'd consider proroguing again in the process. Am I misreading something, or was this indeed a giant slap in the face?