He often portrayed authority figures such as Nazi-era personnel (Secret Army, Colditz, Wish Me Luck and Enemy at the Door) and a British officer (When the Boat Comes In).

[4] Hardiman then toured with the Royal Shakespeare Company[5] in several principal roles, including as Starveling in Peter Brook's landmark 1970 production of A Midsummer Night's Dream.

[7] Hardiman portrayed Major Reinhardt, in Secret Army, the (fictional) head of the Luftwaffe (German Air force) police who often provided a foil to Clifford Rose's more brutal S.S. Chief, Kessler.

[8] A notable small role Hardiman played was a version of the Sergeant Wilson character from Dad's Army, in a 1995 episode of time travel comedy Goodnight Sweetheart, called "Don't Get Around Much Any More."

[8] Hardiman made an appearance on the daily soap on BBC One, Doctors, on 3 April 2009, as well as from 14 to 15 January 2015, and in the drama from Yorkshire, Heartbeat, as John Upton in one episode.

[10] In 2009, he appeared in a film for the BFI, Radio Mania: An Abandoned Work, directed by British artists Iain Forsyth and Jane Pollard.