Stephen Tierney of Edinburgh University outlines the Supreme Court's decision.
This unanimous decision is remarkable for its significance, the speed at which it was arrived at and the strident tone of the judgment. The Supreme Court in one sense upholds the Inner House decision not only that the advice to prorogue was unlawful but that the consequent Order in Council is null and of no effect. It does so however on different grounds, calling upon what it takes to be fundamental constitutional principles rather than the standard grounds of judicial review.
The line of reasoning is very straightforward. Prerogative powers are reviewable; the prorogation power is no different in this respect; there is a fundamental constitutional principle which the court calls ‘Parliamentary accountability’; and it is unlawful to exercise the power to prorogue in a way contrary to this principle: ‘a decision to prorogue (or advise the monarch to prorogue) will be unlawful if the prorogation has the effect of frustrating or preventing, without reasonable justification, the ability of Parliament to carry out its constitutional functions as a legislature and as the body responsible for the supervision of the executive.’
This is not a purposive test but is met simply by the effect of prorogation. In the circumstances the current prorogation met this test. The court justifies this conclusion not only because Parliament is prorogued for five weeks but, crucially, by taking Brexit into account. In light of impending withdrawal on 31st October ‘Parliament, and in particular the House of Commons as the elected representatives of the people, has a right to a voice in how that change comes about. The effect upon the fundamentals of our democracy was extreme.’ The Court also took the view that no valid reasons had been given for the prorogation.
Two other points are notable. First that court concludes that the prorogation is not a proceeding in Parliament. ‘Quite the reverse: it brings that core or essential business to an end.’ And secondly, it is strident in its final finding in law: that the Order in Council to which it led was also unlawful, void and of no effect and should be quashed. The order was in effect a ‘blank sheet of paper’. Therefore, as a matter of law. ‘Parliament has not been prorogued.’
It is impossible to see how as a matter of constitutionalism or politics there is now any alternative for the Prime Minister other than the immediate reconvening of Parliament. What the implications of this decision are for Parliament, its relationship to the Crown and the constitutional role of the judiciary will take much longer to digest.