## Facts

- The case concerned whether the government could invoke Article 50 of the Treaty on European Union to begin the UK's withdrawal from the EU without an act of Parliament.
- The European Union (Withdrawal) Act 2018 was not in force at the time.
- The government argued it had prerogative powers to start Article 50, which would lead to changes in domestic law by ending the operation of the European Communities Act 1972 and affecting rights derived from EU law.
- Claimants, led by Gina Miller, contended that such fundamental changes to UK law and statutory rights required parliamentary approval, as government prerogative powers could not override Parliament’s authority.
- The matter became central to the constitutional relationship between executive power and parliamentary sovereignty during the Brexit process.

## Issues

1. Whether the government could use its prerogative powers to trigger Article 50 TEU and begin the process of leaving the EU without parliamentary authorization.
2. Whether the use of Article 50 would result in changes to domestic law and abrogate rights granted under the European Communities Act 1972 without parliamentary scrutiny or approval.

## Decision

- The Supreme Court ruled that triggering Article 50 would fundamentally alter domestic law and remove statutory rights under the European Communities Act 1972.
- The Court held that the government could not use its prerogative powers to trigger Article 50; parliamentary approval was required.
- It reaffirmed that while the executive manages international affairs, it may not use this power to change domestic law without an act of Parliament.
- The decision imposed strict limits on the scope of executive power regarding changes to UK law.

## Legal Principles

- Parliamentary sovereignty: Parliament is the supreme law-making authority in the UK.
- The executive cannot alter domestic law or abrogate rights created by statute through prerogative powers alone.
- Constitutional principles require significant legal changes—especially those affecting statutory rights—to have parliamentary approval.
- There is a clear distinction between the executive’s power in foreign affairs and its inability to override Parliament with respect to domestic law.

## Conclusion

The Supreme Court’s judgment in Miller established that the government may not unilaterally trigger Article 50 TEU to withdraw from the EU; an act of Parliament is necessary for any changes affecting domestic law and statutory rights, thereby reinforcing the supremacy of Parliament in the UK constitutional structure.

R (Miller) v Secretary of State for Exiting the European Union [2017] UKSC 5