The referendum on leaving the EU continues to reverberate through the political and legal system. Although a 51.9% majority voted to leave the bloc, majorities in both Scotland (62%) and Northern Ireland (55.8%) voted to remain.
That referendum did not, however, settle the legal process for leaving the EU. The highest source of law here is an Act of Parliament - a bill approved by the House of Commons and House of Lords. A referendum does not necessarily have a legal effect. Or in other words, the referendum was merely advisory.
Leaving the EU is to be done through Article 50, which states: "Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements."
However, the country has no single text that contains the constitution, rather the constitution is found across Acts of Parliament, case law, political customs (conventions) and other sources. It is often called unwritten or uncodified, so it was unclear what the UK's "own constitutional requirements" were. This is what the Supreme Court, by an eight to three majority, has now decided.
Westminster argued that it could invoke Article 50 using its prerogative powers. Prerogative powers are the relics of royal power. They can be used by the Government and are important in areas such as foreign affairs. They are inferior to an Act of Parliament, so an act can abolish or suspend prerogative powers.
This was the question for the Supreme Court: could the Government use prerogative powers to trigger Article 50, or was it precluded from doing so by an act or acts or some other source? And if an Act of Parliament is required, must Parliament consult with or get the consent of the devolved assemblies?
All eight majority judges authored the majority judgment, and their reasoning on the prerogative argument is a largely traditional interpretation of UK law, even if it disappoints the Government and a number of others.
The Supreme Court ruled unanimously that there was no legal requirement that Parliament get the approval of or consult with the devolved assemblies.
The Supreme Court recognised that there is a convention that requires Parliament to get consent from the devolved bodies before legislation is passed. However, the court was also clear that as a convention, this is a political matter, and the courts do not enforce conventions.
The Supreme Court approach is in many ways very traditional. This lends strength to its main ruling that the Government cannot trigger Article 50 without an Act of Parliament.
The traditional suggests that neither the process of devolution to Scotland, Wales and Northern Ireland, nor the adoption of unique constitutional arrangements in Northern Ireland, has changed how the courts decide constitutional questions.
This judgment, or rather and more importantly the Brexit vote itself, has exposed serious tensions between the traditional UK constitution and the constitutional settlement in Northern Ireland.
In the short and medium term, Northern Ireland political parties and civil society will have to develop political strategies to ensure that Northern Ireland's interests are represented at all stages and levels as the Brexit process moves forward.
Rory O'Connell is professor of human rights and constitutional law and Director of the Transitional Justice Institute, Ulster University