R (on the application of Miller) v Secretary of State for Exiting the European Union

In R (on the application of Miller) v Secretary of State for Exiting the European Union (2017), the UK Supreme Court ruled that Prime Minister May could not trigger Brexit (Article 50) using executive power alone. Instead, Parliament's approval was necessary because starting the process of leaving the EU would change UK law and rights. The court emphasized that constitutional changes require parliamentary authorisation, reinforcing Parliament’s sovereignty over major constitutional decisions and limiting the Prime Minister’s powers in this context.