He appeared in a number of programmes, but is best known for the role of Private Walker, a cockney spiv, in the BBC sitcom Dad's Army from the show's beginning in 1968 until his sudden death in 1973.

He also appeared, uncredited, as a policeman in Gideon's Way (1965), and was often seen in TV drama, with one-off roles in series such as The Troubleshooters (1965, 1967, 1970) and in 1968, with Peter Cushing in the episode "The Blue Carbuncle", the BBC's Sherlock Holmes.

[8] He also recorded a pilot for an uncommissioned series called Bunclarke With an E (1973),[8] which was to be based on scripts originally written for Hancock's Half Hour and in which Arthur Lowe was also to appear.

[8] All of the location filming and studio recording for five of the planned seven episodes of Series Six had been completed when Beck suddenly fell ill while opening a school fête in aid of Guide Dogs for the Blind.

[8] In the episode, "The Recruit" (the series 6 finale), Mainwaring reads a note written by Walker apologising for his absence, as he has gone "up to the Smoke" (to London) to conduct one of his deals.