The flag of Surrey is the blue and gold chequered flag of the traditional county of Surrey and is derived from the coat of arms of William de Warenne, 2nd Earl of Surrey who adopted arms similar of the Capetian Count of Vermandois on his marriage to Elizabeth, Countess of Leicester (died 1138), who was first married to Robert de Beaumont, 1st Earl of Leicester.
Similar arms were also adopted by his brother in law, Ralph I de Beaugency, who married Hugh I's oldest daughter, Matilda.
The Surrey flag is a representation of the arms originally used as a personal heraldic device by William de Warenne, secound Earl of Surrey, and has since enjoyed a long association with the county itself, as attested to in a 17th-century poem about the Battle of Agincourt.
An early reference of the arms is found in the 13th-century Glover's Roll of Arms, where an account of the siege of Caerlaverock Castle (from 1300) describes the actions of John de Warenne, 6th Earl of Surrey and includes a reference to his banner of blue and gold cheques: "his banner with gold and azure, was nobly chequered”.
The de Warenne family became extinct in the male line in 1347 but, importantly, there is evidence the design continued to be used by the men of the county, as found in a poem about the Battle of Agincourt in 1415 by Michael Drayton (written in 1627) which records the men of Surrey carrying a banner of gold and blue checks into battle in honour of their late earl, "The men of Surrey, Checky Blew and gold, (Which for brave Warren their first Earle they wore".