The Union Flag, or Union Jack, is the national flag of the United Kingdom and it is so called because it embodies the emblems of the three countries united under one Sovereign - the kingdoms of England and Wales, of Scotland and of Ireland (although since 1921 only Northern Ireland has been part of the United Kingdom). The term Union Jack possibly dates from Queen Anne's time (reigned 1702-14), but its origin is uncertain. It may come from the 'jack-et' of the English or Scottish soldiers; or from the name of James I who originated the first union in 1603, in either its Latin or French form Jacobus or Jacques; or, as 'jack' once meant small, the name may be derived from a royal proclamation issued by Charles II that the Union Flag should be flown only by ships of the Royal Navy as a jack, (a small flag at the bowsprit). The flag consists of three heraldic crosses: The cross of St George, patron saint of England since the 1270's, is a red cross on a white ground. It was the national flag of England until James I succeeded to the throne in 1603, after which it was combined in 1606 with the crosses of St. Andrew and St. Patrick; The cross saltire of St Andrew, patron saint of Scotland, is a diagonal white cross on a blue ground.
The cross saltire of St Patrick, patron saint of Ireland, is a diagonal red cross on a white ground. This was combined with the previous Union Flag of St George and St Andrew, after the Act of Union of Ireland with England (and Wales) and Scotland on 1 January 1801, to create the Union Flag that has been flown ever since.
The Welsh dragon does not appear on the Union Flag. This is because when the first Union Flag was created in 1606, the Principality of Wales by that time was already united with England and was no longer a separate principality.
The Union Flag was originally a royal flag (when the present design was made official in 1801, it was ordered to be flown on all the King's forts and castles, but not elsewhere); it is today flown above Buckingham Palace, Windsor Castle and Sandringham when the Queen is not in residence. The Royal Arms of Scotland (“Lion Rampant”) is flown at the Palace of Holyroodhouse and Balmoral when The Queen is not in residence. On news of a Royal death, the Union Flag (or the Royal Arms of Scotland [Lion Rampant] where appropriate) will be flown at half-mast. The Royal Standard is never flown at half mast, as the Sovereign never dies (the new Monarch immediately succeeds his or her predecessor).
The flying of the Union Flag on public buildings is decided by the Department for Culture, Media and Sport at the Queen's command.
The Union Flag has particular significance to the Armed Forces; therefore it is flied during the annual Trooping the Colour ceremony at Horse Guards Parade on the Sovereign's official birthday, when The Queen as Colonel-in-Chief of each of the five regiments of Foot Guards takes the salute.
The flag is also flown on St David's Day (Wales), St George's Day (England), St Andrew's Day (Scotland), and St Patrick's Day (Northern Ireland)
In the Royal Navy, flags and ensigns assumed the same importance as standards and colours in the Army. Until 1864, fleets were organised into White, Red and Blue squadrons, but in that year Queen Victoria ordered that the White Ensign - the red cross of St George with the Union Flag in the top left-hand corner - should be carried by all ships of the Royal Navy.
The Union Flag is flown on government buildings on days marking the birthdays of members of the Royal family, Commonwealth Day, Coronation Day, as well as on the Queen's official birthday.