High Quality Content by WIKIPEDIA articles! The United Kingdom of Great Britain and Ireland was the formal name and the state form of the United Kingdom from 1 January 1801 until 12 April 1927. It was formed by the merger of the Kingdom of Great Britain and the Kingdom of Ireland, with Ireland being governed directly from Westminster through its Dublin Castle administration. Following Irish independence on 6 December 1922, when the 1921 Anglo-Irish Treaty came into effect, the name continued in official use until it was changed to the United Kingdom of Great Britain and Northern Ireland by the Royal and Parliamentary Titles Act of 1927. The part of the island of Ireland that remained seceded from the United Kingdom in 1922 was succeeded by the state of Ireland in 1937.