The flag of the United Kingom is actually a combination of three flags representing England, Scotland and Northern Ireland.
The English flag is the cross of Saint George. It consists of a red cross on a white background.
The Scottish flag is the cross of St. Andrew. It consists of a white saltire, or diagonal cross, on a blue background.
The Northern Irish flag is the cross of St. Patrick. It consists of a red saltire on a white background.
The colours of the Union Flag of the United Kingdom of Great Britain and Northern Ireland come from a combination of the following:
Cross of St George (representing England): Red cross on a white background
Cross of St Andrew (representing Scotland): White saltire on blue background (added to the flag after the Act of Union between England and Scotland in 1707)
Cross of St Patrick (representing Ireland): Red saltire on white background (added to the flag after the Act of Union between Great Britain and Ireland in 1801)
The Union Flag, sometimes known as the Union Jack, is an amalgamation of the flags of England, Scotland and Northern Ireland.