[3] He is best known for his portrayal of the monster in the 1972 cult British horror movie, Death Line, and as Harry Wax in How to Get Ahead in Advertising, acting alongside Richard E.

[4] Armstrong's first major role was as Ted the chauffeur in the 1968 film Prudence and the Pill, starring David Niven and Deborah Kerr.

[5][4][6] His next major role was playing the monster in Death Line alongside Donald Pleasence and Christopher Lee; his performance was said to have achieved the impossible by making a 'grotesque violent cannibal seem pitiful and sympathetic'.

[4] He appeared as Jun Priest in the 1982 film, The Beastmaster, and played Harry Wax in How to Get Ahead in Advertising alongside Richard E.

McMurphy in One Flew Over The Cuckoo's Nest at the Everyman Theatre in Liverpool alongside Bill Nighy and Julie Walters.