The flag of England is derived from Saint George's Cross (heraldic blazon: Argent, a cross gules). The association of the red cross as an emblem of England can be traced back to the Late Middle Ages, and it was increasingly used alongside the Royal Banner in the wake of the English Reformation, especially as a maritime flag referred to as a white ensign. It was used as a component in the design of the Union Jack in 1606.

It has been widely used since the 1990s, specifically at national sporting events, especially during England's national football team's season.

In 1188 Henry II of England and Philip II of France agreed to go on a crusade, and that Henry would use a white cross and Philip a red cross.[citation needed] Thirteenth-century authorities[who?] are unanimous on the point that the English king adopted the white cross, and the French king the red one (and not vice versa as suggested by later use). It is thus not clear at what point the English exchanged the white cross for the red-on-white one.[according to whom?]

There was a historiographical tradition claiming that Richard the Lionheart himself adopted both the flag and the patron saint from the Republic of Genoa at some point during his crusade. This idea can be traced to the Victorian era, Perrin (1922) refers to it as a "common belief", and it is still popularly repeated today even though it cannot be substantiated as historical. Prince Edward, Duke of Kent repeated this in a bilingual preface to a brochure made for the British Pavilion at Genoa Expo '92. The relevant passage read:

The St. George's flag, a red cross on a white field, was adopted by England and the City of London in 1190 for their ships entering the Mediterranean to benefit from the protection of the Genoese fleet. The English Monarch paid an annual tribute to the Doge of Genoa for this privilege.