European Union
The government of the UK invoked "Article 50" of the Treaty of European Union (the Treaty of Lisbon) on 29 March 2017. This began negotiations with fellow members of the EU on the terms of exit. The timetable for these negotiations is two years, which meant that the UK would remain a member of the EU until at least March 2019. However this deadline was later extended to October 31st 2019 at the request of the British Government. The United Kingdom left the European Union on the 31 of January 2020 at 23:00 (Greenwich Mean Time). Following the UK left from the European Union on January 31, the transition period  expired on December 31, 2020 and ended on January 1, 2021.