R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5
The first Miller case is the leading authority on the relationship between devolution and parliamentary sovereignty. The claimants argued that triggering Article 50 TEU required not only an Act of the UK Parliament but also the consent of the devolved legislatures under the Sewel Convention. The Supreme Court unanimously rejected the argument. The Sewel Convention, though recognised in statute (Scotland Act 2016, s. 2), remained a political convention and was therefore non-justiciable. The Court, in its majority judgment, stated at [151]:
"The policing of its scope and the manner of its operation does not lie within the constitutional remit of the judiciary, which is to protect the rule of law."
The Court emphasised that the devolution statutes preserved Westminster's sovereignty expressly and that the devolved institutions owed their existence and powers to Westminster legislation.
Reference by the Lord Advocate (UK Withdrawal from the European Union (Legal Continuity) (Scotland) Bill) [2018] UKSC 64
This reference concerned the competence of the Scottish Parliament to legislate on retained EU law following Brexit. The Supreme Court held that provisions of the Continuity Bill that purported to create a separate Scottish regime for retained EU law were outside competence because they related to reserved matters (the union of Scotland and England, and UK international relations). The Court reaffirmed that devolved competence is a question of statutory interpretation and that the courts' role is to determine whether legislation is intra vires or ultra vires. The decision underlined the constraints on devolved legislative autonomy, even on matters ostensibly within devolved fields if they touch reserved areas.
Imperial Tobacco Ltd v Lord Advocate [2012] UKSC 61
Imperial Tobacco challenged the Tobacco and Primary Medical Services (Scotland) Act 2010, which banned the display of tobacco products in shops and restricted vending machines. The company argued that the Act related to reserved matters (product standards and regulation of the internal market) and was thus outside competence. The Supreme Court rejected the challenge, holding that the "purpose" test was key: legislation relates to a reserved matter only if it has more than a loose or consequential connection to it. The Act's purpose was public health—a devolved matter—and the effect on reserved matters was incidental. The decision adopted a purposive approach to legislative competence and gave the devolved legislatures considerable latitude.
AXA General Insurance Ltd v Lord Advocate [2011] UKSC 46
Claimants challenged the Damages (Asbestos-related Conditions) (Scotland) Act 2009, arguing it was outside competence and violated common law constitutional principles (the rule of law and property rights). The Supreme Court held that Acts of the Scottish Parliament are subject to judicial review on vires grounds—whether they comply with the Scotland Act 1998—but rejected the notion that the common law imposed freestanding constraints on competent devolved legislation. Lord Hope stated at [51]:
"The rule of law requires that the judges must retain the power to insist that legislation of that extreme kind is not law which the courts will recognise."
However, the hypothetical extreme case did not arise here. The decision clarified that devolved legislation is subordinate legislation for purposes of judicial review, but the grounds of review are limited to those set out in the devolution statute.
Reference by the Attorney General for Northern Ireland—Abortion Services (Safe Access Zones) (Northern Ireland) Bill [2022] UKSC 32
The Supreme Court held that a private member's bill in the Northern Ireland Assembly regulating access to abortion clinics was outside competence. Abortion law had been removed from devolved competence by Westminster legislation (Northern Ireland (Executive Formation etc) Act 2019), which imposed a duty on the Secretary of State to implement new abortion regulations. The Court confirmed that Westminster may alter devolved competence by statute and that such changes bind the devolved legislature.
Christian Institute v Lord Advocate [2016] UKSC 51
This case concerned the Children and Young People (Scotland) Act 2014, which introduced a "named person" scheme assigning a state guardian to every child. Challengers argued the scheme breached ECHR Article 8 (family life) and was thus outside competence (Scotland Act 1998, s. 29(2)(d)). The Supreme Court held that certain provisions of the scheme were indeed incompatible with Article 8 because the statutory framework for information-sharing was insufficiently precise and did not comply with the "prescribed by law" requirement. The decision confirmed that devolved legislation must comply with Convention rights and that non-compliance renders it ultra vires.