The judgment‘s conclusions on the Sewel convention are welcome. Enacting the convention for Scotland had been risky. Would the courts construe it with an irrebuttable presumption of an intention to produce something legally enforceable? It is good that the Supreme Court has accepted that Parliamentary sovereignty involves a freedom to legislate for other purposes, even if it remains risky to do it too often. It is good too that, in this context, the Court has recognised the relevance of Art IX of the Bill of Rights 1688/9 (i.e. that proceedings in Parliament must not be called into question in any court).

It is regrettable that the majority failed to recognise Article IX’s relevance to the main issue. Art IX represents Parliament’s claim for exclusive jurisdiction over its own functions. As is made clear in Lord Carnwath’s dissenting judgement, with its analysis of the proper and established relationships between the courts, Parliament and Government, what was at stake was whether the courts should regulate Parliament’s dealings with Government.

The majority relied, instead, on stopping the “speeding bullet”: the possibility, however unlikely, that the Art 50 notice, once given, would terminate EU membership without further Parliamentary involvement. A preemptive judicial remedy against a highly unlikely illegality is unusual; and it cannot in this case be compatible with the Art IX principle. Parliament can and will insist on exercising its constitutional function. It is already scrutinising the executive’s handling of the negotiations. Reliance in the courts on the speeding bullet idea involves questioning Parliament’s capacity or willingness to do those things, and telling Parliament how they should be done.

The practical impact of the judgment is unclear. There must be an Act the effect of which will give basic legal cover for automatic UK exit when the Art 50 notice expires. Maybe having that already in place will have a small, possibly unhelpful, effect on the process of passing the more detailed legislation for that and other possible forms of exit. Government is already bound to have regard to Parliamentary opinion in the negotiations. Were it not for the future implications of the disregard of the Art IX principle, it is difficult not to join those who, as Lord Carnwath suggests, will regard the case as ”an exercise in pure legal formalism”.

Sir Stephen Laws KCB, QC(Hon), LLD(Hon) is a former First Parliamentary Counsel (2006-2012). He is Senior Associate Research Fellow at the Institute of Advanced Legal Studies, an Honorary Senior Research Associate at University College London and an Honorary Fellow of the University of Kent Law School.

Click here for further analysis of the Supreme Court’s Miller judgment.