The High Court ruled it non-justiciable as inherently political (a similar approach to the 'political question' doctrine in US federal courts). The question th

The High Court ruled it non-justiciable as inherently political (a similar approach to the 'political question' doctrine in US federal courts). The question the Supreme Court grappled with was whether the actual act of prorogation was a "proceeding in Parliament" or not. If it was, then the court can't overturn its effect despite the illegality they found in the earlier parts of the process (advice and Order-in-Council) as proceedings in Parliament are exempt from judicial scrutiny by the Act of Settlement 1688. They ruled that it wasn't (despite happening in Parliament) as prorogation is inherently an executive imposition from outside and therefore not a Parliamentary proceeding. Consequently they could rule the prorogation "void and of no effect" rather than merely making a declaration of unlawfulness or instructing the PM to have Parliament recalled.