Monty Python

In the mid-1970s, Innes became closely associated with the TV series Monty Python's Flying Circus. He played a major role in performing and writing songs and sketches for the final series in 1974 (after John Cleese left). He wrote a squib of a song called "George III" for the episode "The Golden Age of Ballooning", which was sung by The Flirtations, but billed onscreen as the Ronettes). He also wrote the song "When Does a Dream Begin?", used in "Anything Goes: The Light Entertainment War". He co-wrote the "Most Awful Family in Britain" sketch and played a humorous stilted guitar version of the theme song, The Liberty Bell March, during the credits of the last episode, "Party Political Broadcast". He is one of only two non-Pythons to ever be credited writers for the TV series, the other being Douglas Adams (who co-wrote another sketch in "Party Political Broadcast").

He appeared on stage with the Pythons in New York City in 1976, performing the Bob Dylanesque "Protest Song" (complete with harmonica) on the album Monty Python Live at City Center. He was introduced as Raymond Scum. After his introduction he told the audience, "I've suffered for my music. Now it's your turn." In 1982 he travelled to the States with the Pythons again, appearing in Monty Python Live at the Hollywood Bowl. He performed the songs "How Sweet to Be an Idiot" and "I'm the Urban Spaceman". He also appeared as one of the singing "Bruces" in the Philosopher Sketch and as a Church Policeman in that sketch.

Innes wrote the songs for Monty Python and the Holy Grail. He appeared in the film as a head-bashing monk, the serf crushed by the giant wooden rabbit, and the leader of Sir Robin's minstrels. He also had a small role in Terry Gilliam's Jabberwocky. His collaborations with Monty Python and other artists were documented in the musical film The Seventh Python (2008).