While not a member of the Beatles, Neil Innes was a well-known musician who was heavily influenced by them and was often associated with their work. He wrote several songs for the Rutles, a parody band created by the Pythons that was a send-up of the Beatles.
In the film, Innes appears as a Roman centurion, and sings a song called "The Life of Brian," which is a satirical take on the Beatles' hit "The Life of Riley."