Revenue stamps of Northern Ireland
Upon the partition of Ireland in 1921, separate revenue stamps began to be issued for both Northern Ireland and Southern Ireland. The latter were withdrawn soon afterwards upon the establishment of the Provisional Government, but the former continued to issue revenue stamps until the late 20th century. The need for separate issues for Northern Ireland came about since taxes raised there were meant to remain in the country. Most Northern Irish revenue stamps were British key types with appropriate inscriptions, but there were a number of different issues as well.
History of the United Kingdom
In 1922, Catholic Ireland seceded to become the Irish Free State; a day later, Northern Ireland seceded from the Free State and returned to the United Kingdom. In 1927 the United Kingdom changed its formal title to the "United Kingdom of Great Britain and Northern Ireland," usually shortened to "Britain" and (after 1945) to the "United Kingdom" or "UK".