The United Kingdom has been a WTO member since 1 January 1995 and a member of the General Agreement on Tariffs and Trade (GATT) since 1 January 1948. Until 31 January 2020, it was a member state of the European Union. The European Union and the United Kingdom have agreed a Withdrawal Agreement pursuant to Article 50 of the Treaty on European Union, which provides for a time-limited transition period during which European Union law, with limited exceptions as provided for in the Withdrawal Agreement, will apply to and in the United Kingdom.

The communication from the United Kingdom states that the transition period provides continuity in the trading relationship between the United Kingdom and the European Union, and with other WTO members, with the United Kingdom remaining part of the European Union's customs union and single market during that time.
 

Source: Vitic/ wto.org