The enforcement of EU environmental law is of particular relevance because EU law provides most of the framework of environmental law in the Member States, including the UK. Supervision by the EU Commission ensures a certain general standard of compliance, especially as regards transposition of directives and conformity of transposing legislation. The practice of domestic courts is an essential complement to Commission action. In this respect the Luxembourg jurisprudence has in particular strengthened the judicial powers of UK courts and provided some protection against excessive costs of judicial proceedings. After brexit much of this contribution could continue to be relevant, in particular if the agreement that was negotiated with the EU should be ratified.