John Alderton married his co-star, Jill Browne, but they later divorced. After an uncredited role in "Cleopatra" (1963), and appearing in British films such as "The System" (1964), "Assignment K" (1968), "Duffy" (1968) and "Hannibal Brooks" (1969), he played the lead in the comedy series "Please Sir!", as hapless teacher Mr Hedges, which later resulted in him also playing the character in the 1971 feature film of the same name. In 1972 he appeared with Hannah Gordon in the BBC comedy series "My Wife Next Door" which ran for 13 episodes, and for which he won a Jacob's Award in 1975. He
John Alderton then transferred to another top-rated ITV series when he played Thomas Watkins, the chauffeur, in "Upstairs, Downstairs", opposite his wife, Pauline Collins. They had a daughter (the actress Kate Alderton) and two sons and also acted together in spin-off series, "Thomas & Sarah", and another sitcom, "No, Honestly", as well as in "Wodehouse Playhouse" (1975–78), a series that featured adaptations of short stories by P. G. Wodehouse (primarily the "Mr. Mulliner" stories.) In the meantime, he appeared on the big screen against-type as 'Friend' in John Boorman's cult sci-fi film "Zardoz" (1974), before returning to more familiar territory, as 1930s