Thornton was best known for playing Captain Peacock in the long-running BBC comedy series "Are You Being Served?" from 1972 to 1985. He reprised his role for "Grace & Favour" from 1992 to 1993. In 1984 he starred as Sir John Treymane in the hit London musical "Me and My Girl", earning rave reviews and an Olivier Award nomination. He also guest-starred in an episode of the BBC Radio series of "Dad's Army" entitled "Ten Seconds from Now" as the BBC producer Willoughby Maxwell-Troughton, who has to coordinate the chaotic platoon as it tries to broadcast to the nation in a morale-boosting Gang Show-style extravaganza. In 1980 he joined John Cleese in the BBC Television Shakespeare production of "The Taming of the Shrew".