On 29 March 2017, the United Kingdom officially notified the European Council of its intention to leave the European Union, thus activating Article 50 of the Treaty on European Union.
A two-year period began during which the European Union and the United Kingdom had to negotiate an agreement that would regulate the withdrawal and their future relationship, in order to achieve an orderly exit.
After several years of negotiations, on 1 February 2020, once the ratification process of the Withdrawal Agreement was completed by both parties, the United Kingdom left the EU and became a third country. This marked the beginning of a transitional period.
During the transitional period, the acquis communautaire continued to apply to the United Kingdom, and negotiations to reach a new agreement that would set the terms of the UK-EU future relationship after the transitional period were conducted. In fact, on 24 December 2020, the Trade and Cooperation Agreement was reached between the European Union and the European Atomic Energy Community, on the one hand, and the United Kingdom of Great Britain and Northern Ireland, on the other hand.
Thus, as of 1 January 2021, after the transitional period, the Trade and Cooperation Agreement is applicable, which is the one that regulates future relations between the United Kingdom and the European Union.