The film is based on a true episode, the Archer-Shee case. Sir Robert Morton in real life was Sir Edward Carson, an Irish Tory politician and brilliantly histrionic lawyer who successfully defended the boy, who was the half-brother of a fellow MP. Carson later married a much younger woman, though not the boy's sister. The Winslow Boy himself was killed during the First World War.
Review of The Winslow Boy
