The immediate consequences of the Supreme Court decision in Miller are already being actioned, with the Article 50 Bill making its way through the Houses of Parliament. However the decision also considers a range of constitutional principles that will impact other cases for years to come. While there has been plenty of coverage on the immediate effects on Brexit, we comment here on what other effects the Miller decision may have.
The Supreme Court has clearly focussed on what is and is not within their constitutional remit. The Government's arguments made much of various ministerial statements since the referendum about the planned process for triggering Article 50. There were various submissions on the power of such statements, especially when given in Parliament, however Lord Neuberger's decision is clear that Government or ministerial intention cannot be the basis for any court rulings, which can only be based on law.
This principle also extends to other forms of government intent. While there was less coverage of devolution issues than some of the parties may have hoped for (the finding that an Act of Parliament was needed for Article 50 rendered many of the devolution arguments moot), the Supreme Court did address the legal status of the Sewel Convention. The Sewel Convention, established during the passing of the Scotland Act 1998 and later enshrined in the same Act, states that Westminster "will not normally legislate with regard to devolved matters without the consent of the Scottish Parliament." However, in Miller the Supreme Court found that, while the convention may be a political restriction on the actions of the UK Parliament, it was not a matter for the courts to enforce it. This again sets out clear boundaries between the work of Parliament and its internal norms, and the true principles of constitutional law.
Another aspect of the decision makes clear that referenda are a very new part of our political and constitutional landscape, and they are not yet a feature of our constitutional law. Last year's referendum was only the third national referendum, and as such their implementation has not yet been fully explored by the courts. The Supreme Court found that a referendum in and of itself was not enough to give legal effect to the outcome. While the Act leading to the 2011 referendum on electoral reform had included provision for the outcome to be enforced in law, there was no such provision for the Brexit referendum. As such the result was not capable of giving the Government the power required to trigger Article 50.
More broadly, the decision has strongly reinforced the separation between the spheres of the executive and Parliament. Lord Neuberger was clear that prerogative powers can only be used when it will not breach or change domestic law, i.e. only when Parliament has not legislated on the matter. While at first glance the decision to leave the EU was a decision of international law, the unprecedented effect the EU has had on domestic law means that the decision to leave would automatically affect domestic law, according to the majority judgement. Even if Parliament voted on the final deal after the two-year period of negotiation, by that point domestic law would have to be changed (on the premise adopted by the parties that Article 50 notification cannot be rescinded) so Parliament's hand would be forced.
The immediate coverage of the Miller decision at the time was understandably focussed on how to trigger Article 50. Now that this is being implemented, the broader implications of the decision will be reviewed more closely. To decide the relatively narrow point of Article 50 the Supreme Court has covered considerable constitutional ground, and their findings will doubtlessly affect future judgments for many years to come.