R (on the application of Miller and another) v Secretary of State for Exiting the European Union  UKSC 5
In an historic appeal, all eleven Justices sat together for the first time to hear an appeal from a decision of the High Court that the Secretary of State for Exiting the European Union did not have the power to serve notice of the UK’s intention to withdraw from the EU without prior authorisation by an act of Parliament. The appeal required the court to consider the UK’s constitutional requirements, which were a matter of domestic law which all parties agreed should be determined by UK judges. The appeal was joined with two references from Northern Ireland raising additional issues of whether the terms on which powers had been devolved required consultation with or the agreement of the devolved legislature or otherwise operated to restrict the Government’s power to serve such notice. The Lord Advocate and Counsel General on behalf of the Scottish and Welsh governments respectively intervened in the appeal. There were three further interveners and two interested parties. The Supreme Court, by a majority of 8 to 3, dismissed the Secretary of State’s appeal, holding that the terms of the European Communities Act 1972, which gave effect to the UK’s membership of the EU, were inconsistent with the exercise by ministers of any power to withdraw from the EU treaties without authorisation by a prior Act of Parliament. The dissenting judges would have held that the effect of the 1972 Act was conditional on the UK’s membership of the EU and did not affect the Crown’s prerogative power to withdraw from international treaties. On the devolution issues, the justices unanimously concluded that any obligation to consult the devolved institutions operated as a political rather than a legal constraint on the activity of the UK Parliament, the policing of which was not within the constitutional remit of the courts.