The following flags represent United Kingdom (Great Britain) or one of its predecessors. These flags can be used as is or as inspiration.
See also: Flags of England, Flags of Scotland, Flags of Ireland, Flags of Wales and Flags of Northern Ireland.
OTL British Flags
Historical
The English version of the Union Flag (1606-1707), also flag of the Kingdom of Great Britain (1707-1801)
The Scottish version of the Union Flag (1606-1707)
Flag of the Protectorate (Commonwealth of England, Scotland and Ireland) between 1658 and 1660.
The White Ensign (also know as the St George's Ensign), flag of the Royal Navy
The British Red Ensign (1707–1801)
The Red Ensign, flag of the British Merchant Marine. Often defaced for use by colonies/nations, namely Canada
The Blue Ensign, the flag of the British government. Often defaced for use by colonies/nations, namely Australia and New Zealand
ATL
The Union flag as pictured by James Gillray
United Kingdom of Britain, Ireland and Germany
This is a flag that represents every country within the UK.
The Republic of the British Isles
Union Jack with the flag of Saint David (Wales) added.
Union Jack with the flags of Saint David (Wales) and Saint Piran (Cornwall) added.
Union Jack without Scotland, blue replaced with black to represent Wales instead.
Union Jack Variant with Wales Added
Cromwellian Republican Flag
Moderate British Republican Flag
Anglo-Dutch
Modern Versions
Union of United Kingdom
Other UK Unions
Subdivisions
Colonial flag of a fictional island
Colonial Flags