What flag represents the United Kingdom?

The flag that represents the United Kingdom is the Union Jack. The Union Jack is a combination of the flags of England, Scotland, and Ireland, symbolizing the unity of these nations. It features the cross of St. George for England, the cross of St. Andrew for Scotland, and the cross of St. Patrick for Ireland, all integrated into one design.

This flag is not only a national symbol but also often used in various official capacities by the government and other institutions in the UK. The other flags mentioned, while associated with the UK or its regions, do not represent the United Kingdom as a whole in the same way the Union Jack does. The British Standard is primarily a flag of the British monarch, the Royal Banner is specific to the reigning monarch's standard, and the Commonwealth Flag represents the Commonwealth of Nations rather than the UK itself.