At the end of 2023, the Retained EU Law (Revocation and Reform) Act 2023 (REUL Act) made significant changes to retained EU law, which is known as assimilated law as regards all times after the end of 2023, but continues to be known as retained EU law as regards all times at or before the end of 2023.
Retained EU law comprises the following (subject to various exceptions), together with the interpretations of it by the UK courts and any additions and modifications made to it by domestic law from time to time (section 6(7), EUWA):
EU-derived domestic legislation: the domestic legislation which continues to be domestic law under section 2 of the EUWA, such as UK legislation that implemented EU directives or relates otherwise to the EU or the European Economic Area (EEA).
Retained direct EU legislation: the EU-derived legislation which was converted into domestic law by section 3 of the EUWA, such as UK versions of EU regulations and EU decisions which were directly applicable in domestic law immediately before the end of the transition period.
EU-derived rights and obligations (etc) which were converted into domestic law by section 4 of the EUWA, such as directly effective rights in EU treaties. Although section 4 was repealed at the end of 2023, section 4 continues to be enforceable in relation to anything occurring before the end of 2023.