Britain itself, as a nation, has not experienced colonization by another country or gained independence in the way many former colonies have. However, if you're referring to the independence of individual countries within the British Isles, then the Republic of Ireland (now simply known as Ireland) gained its independence from the United Kingdom in 1922, following the Anglo-Irish Treaty. This marked the establishment of the Irish Free State, which later became the Republic of Ireland.
As for the United Kingdom, it remains a sovereign state and has not sought independence in the same manner as its former colonies. The United Kingdom comprises England, Scotland, Wales, and Northern Ireland, and it has its own unique history and political dynamics.