Film
* The Day of the Jackal (1973) - As the voice of the narrator, this film earned Forbes a BAFTA Award nomination for Best Supporting Actor.
* The Odessa File (1974) - Played the role of Peter, a journalist who helps a survivor of a Nazi massacre.
* The Four Feathers (1978) - Played the role of Colonel Hadock, a British officer in Sudan.
* The Wild Geese (1978) - Played the role of Captain Jones, a member of a mercenary group.
* The Elephant Man (1980) - Played the role of Mr. Ross, the hospital's board secretary.
* The Jewel of the Nile (1985) - Played the role of General Omar.
* The Fifth Element (1997) - Played the role of the Supreme Leader.
* The Last Legion (2007) - Played the role of King Lucius Septimius Severus.
Television
* The Avengers (1961-1969) - Appeared in several episodes.
* The Saint (1962-1969) - Appeared in several episodes.
* The Professionals (1977-1983) - Played the recurring role of Colonel Alistair Reynolds.
* Minder (1979-1994) - Played the recurring role of Freddie.
* The Jewel in the Crown (1984) - Played the role of Dr. Reginald.
* The Bourne Identity (2002) - Played the role of a CIA officer.
* The Bill (1984-2010) - Appeared in numerous episodes.
* Holby City (1999-2022) - Played the recurring role of Father Michael.
This list is not exhaustive, but it highlights some of Forbes's most significant and memorable roles. He has also appeared in many other films and television series throughout his long and successful career.