This chapter focuses on the current interaction between European Union and UK law. EU law is currently a source of UK law. However, the relationship between the two regimes is expected to change in the future as a consequence of the UK’s decision to withdraw from the EU. The European Union (Withdrawal) Act 2018 stipulates that the European Communities Act 1972 will be ‘repealed on exit day’, which would be 29 March 2019 provided that the two-year period since Article 50 TEU was triggered is not extended. Once the European Communities Act 1972 has been repealed, EU law will cease to be a source of UK law. No major immediate changes to the national competition legislation are to be expected, but future reforms could distance the UK system from the EU rules.