Queen Elizabeth's coffin is draped in the Royal Standard before her funeral service in Westminster Abbey on Monday.
The flag represents the sovereignty of the monarch and is flown only at royal residences while they are present, or on their vehicles as they travel to other locations.
After his mother's death, only the reigning monarch, King Charles III, is allowed use of the flag.
The flag has been draped on the queen's coffin on the catafalque as she lies in state, and placed upon it is the Imperial State Crown, and the sceptre and orb.
It will be removed before her burial in Windsor at 4pm on Monday.
Officially, two versions of the standard exist: one for use in England, Wales, Northern Ireland and other territories, while the other is solely for use in Scotland.
The banner is split into four equal quadrants, each representing three nations of the UK, including Northern Ireland and Scotland.
The three lions passant guardant is the traditional symbol of England and is typically seen in the first and fourth quadrant.
The lion rampant represents Scotland while the harp, the traditional symbol of Ireland, represents Northern Ireland.
Wales does not feature on the flag, because of its constitutional status as a principality. However, standards used by other royals sometimes feature Welsh symbols.
While in Scotland, a variation of the flag is used where the first and third quadrants are replaced with the Scottish lion rampant symbol.
The queen's coffin was draped in this variation as it was taken from her Scottish residence in Balmoral to England before her funeral.
Other members of the royal family have their own variation of the flag, including Prince Harry, whose standard includes a red escallop taken from the arms of the house of Spencer, which his mother Diana belonged to.