Lamont also appeared in guest roles in a range of popular British programmes from the 1950s to the 1970s, including The Adventures of Robin Hood, Dixon of Dock Green, Danger Man, The Avengers, Randall and Hopkirk (Deceased), The Persuaders! and Doctor Who.
In 1953, he appeared in the major role of Astronaut Victor Carroon in Nigel Kneale's ground-breaking BBC science-fiction serial The Quatermass Experiment, and fourteen years later returned to the series when he played the role of Sladden in the Hammer Films version of the third serial, Quatermass and the Pit.
From 1958 to 1960, Lamont was a semi-regular as David MacMorris in the CBS western television series, The Texan, starring Rory Calhoun.
On film, the best-known of the many productions he appeared in were The 39 Steps (1959, as Kennedy), Ben-Hur (1959, uncredited but playing Marius), Mutiny on the Bounty (1962, as John Williams), Arabesque (1966) and Battle of Britain (1969, as FLIGHT Sergeant Arthur). Lamont is particularly memorable in his role as the wry, urbane Viceroy in Jean Renoir's The Golden Coach.
He died in 1978 in Tunbridge Wells, Kent, of a heart attack at the age of sixty. He was working at the time on "Hostage", an episode of the BBC science-fiction series Blake's 7. Although he had completed location work for the episode, he died before the studio scenes had been shot, necessitating a re-mount of the location material in which he appeared and his replacement by the actor John Abineri.
