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British History Online: Hundred of South Erpingham: Calthorp

"Dated at Westminster, July 24. Sir William married Cecilia, daughter of Sir Phillip, and sister and heir to William de Burnham, alias Warren, descended(as it is said) from a cousin-german of Hameline Plantaginet Earl Warren and Surrey, and bore for his arms, checque, or and azure, a fess ermine. Some take them to be the arms of the De Burnhams, alias Warren, a younger branch of the Earl Warren's, (fn. 4) which Sir William Calthorpe took up on his marriage with Cecilia aforesaid; but it is more probable the Calthorps bore them, as dependants on the Earls Warren, their capital lords, under whom they held several lordships; and it appears that Walter the Bishop, and uncle to this William, bore the same; and in the 30th of Henry II. when a fine was levied between Matthew de Gourney, and Rose his wife, and Phillip de Burnham, of the manor of Harpley, before John Bishop of Norwich, and Adam de Glanvil, the King's justices, Phillip's seal was the same with that of Hameline Earl Warren; this Sir William Calthorp, and Sir Ralph de Hemmenhale were founders of Burnham priory in 1241.

Sir Walter de Calthorp was his son and heir, by Cecilia, and married Ela, daughter of Sir Hervy Stanhowe, lord of Stanhowe; who bore barry of eight, azure and or, a bend over all gules; they are both mentioned in a fine in the 14th and 25th of Edward I. in which last year he gave land at Burnham to the priory; and in the 11th of Edward II. he quitted claim to Henry, abbot of Holm, certain services due to him for tenements in Beston, and sealed as his father; witnesses Sir Jeffery Wyth, Sir Roger Jenney, Sir Reginald le Gross, &c.; and died about the 17th of Edward II. His successour, by the name of Sir William Calthorp, son of Sir Walter..."

[https://www.british-history.ac.uk/topographical-hist-norfolk/vol6/p...]