Clark was the son of a master builder in Maida Vale, and was educated nearby at St Marylebone Grammar School. After leaving school he became a reporter on a local newspaper in Croydon. He had always wanted to be an actor and when offered a job with the local rep, he took it and apart from six years in the army, he remained in the profession. His first stage appearance was at the Festival Theatre, Cambridge, and he went on to appear in plays at both the West End in London, and Broadway in New York. In 1955 he appeared on stage in Witness for the Prosecution at Henry Miller’s Theatre in New York City, and on film as Air Vice-Marshal The Honourable Ralph Cochrane AFC RAF, AOC, No. 5 Group RAF in The Dam Busters (1955). He is perhaps best remembered for his role as the irascible Professor Geoffrey Loftus in the television comedy series Doctor in the House and its sequels, apart from Doctor at Sea, in which he appeared as Captain Norman Loftus (the brother of Professor Loftus). He also appeared as the Dean in the BBC sitcom All Gas and Gaiters (1967–71). Clark was President of the actors’ trade union, Equity, from 1969 to 1973. He married three times: one of his wives was actress Avril Hillyer, the first two marriages were dissolved. His third marriage, from 1972 until his death, was to Julia Lockwood (née Margaret Julia Leon in 1941), the actress daughter of the British film star Margaret Lockwood, with whom he had four children, Tim, Nicholas, Lucy and Katharine. He died 11 November 1994 in Hinton St. George, Somerset, aged 82.