The UK was treated for most purposes as if it were still an EU member state, but did not have the rights of an EU member state to participate in the EU institutions, bodies, offices and agencies. All the usual EU supervisory, judiciary and enforcement mechanisms continued to apply, including the jurisdiction of the Court of Justice of the European Union.

Most EU law (including as amended or supplemented) continued to apply to the UK, and references to EU member states in that EU law were understood as including the UK (see Practice note, UK law during the post-Brexit transition period: overview).

The UK was bound by the obligations stemming from the EU's international agreements (see Practice note, Brexit: application of international agreements to the UK).

Definition of "transition period" in the withdrawal agreement: the period provided in Article 126 (Article 2(e), withdrawal agreement).

Definition of "IP completion day" in the European Union (Withdrawal Agreement) Act 2020 (WAA): 31 December 2020 at 11.00 pm (section 39(1), WAA). IP completion day has the same meaning in the European Union (Withdrawal) Act 2018 (EUWA) (section 1A(6), EUWA). If any Act of Parliament uses the term "IP completion day", this has the same meaning as in the WAA unless the contrary intention appears (section 5 and paragraph 1, Schedule 1, Interpretation Act 1978).