Revenue stamps of the United Kingdom
When Ireland was partitioned into Northern Ireland and Southern Ireland in 1921, separate revenue stamps were issued for both entities. Southern Ireland stamps saw little use since that political entity was quickly superseded by the Provisional Government of Ireland and later the Irish Free State (both of which applied overprints on various British and Irish revenue stamps). However, Northern Ireland continued to use separate revenue stamps until the 1980s. Northern Irish revenues include Civil Service, Dog Licence, Excise and National Insurance stamps, among many others.
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".