Question: Who co-wrote the 1971 British comedy film "On the Buses"?

Context paragraphs:
The Statue (1971 film): The Statue is a 1971 British comedy film starring David Niven, Robert Vaughn and Italian beauty Virna Lisi directed by Rodney Amateau.  Monty Python's John Cleese and Graham Chapman appear in early roles as the Niven character's psychiatrist and a newsreader respectively.  Niven plays a nobel-prize winning professor who suspects his wife, played by Lisi, of infidelity when she makes and unveils an 18-foot statue of him with private parts recognisably not his own.  The film is based on the play called "Chip, Chip, Chip" by Alec Coppel.

Percy (film): Percy is a 1971 British comedy film directed by Ralph Thomas starring Hywel Bennett, Denholm Elliott, Elke Sommer and Britt Ekland.

Mutiny on the Buses: Mutiny on the Buses is a 1972 British comedy film directed by Harry Booth and starring Reg Varney and Doris Hare.  The film is the second spin-off film from the TV sitcom "On the Buses" and succeeded "On the Buses" (1971).  It was followed by a third film "Holiday on the Buses" (1973).  The film was produced by Ronald Chesney and Ronald Wolfe for Hammer Films.  "Mutiny on the Buses" came 17th in the 1972 box office.

Please Sir! (film): Please Sir!  is a 1971 British comedy film starring John Alderton, spun off from the television series "Please Sir! "

Geoff Unwin: Geoff Unwin (born 8 October 1936) is an English musician and composer.  He is best known for his early association with and promotion of the Mellotron, a tape-based sampling keyboard, and for co-writing the theme music for the first "On the Buses" film.

She'll Follow You Anywhere: She'll Follow You Anywhere, released in the United States as Passion Potion, is a 1971 British comedy film directed by David C. Rea and starring Kenneth Cope, Keith Barron and Richard Vernon.  The screenplay concerns two chemists working in a lab of a big corporation who accidentally stumble across a love potion while working to create a new aftershave.  The potion makes a man irresistible to any woman who smells it.  However, they soon have problems remembering the formula, and keeping their discovery from their bosses and wives.

Games That Lovers Play: Games That Lovers Play is a 1971 British comedy film written and directed by Malcolm Leigh and starring Joanna Lumley, Penny Brahms and Richard Wattis.

Holiday on the Buses: Holiday on the Buses is a 1973 British comedy film directed by Bryan Izzard and starring Reg Varney and Doris Hare.  The film is the third and final spin-off film from the ITV sitcom "On the Buses" and succeeded the films "On the Buses" (1971) and "Mutiny on the Buses" (1972).  The film was produced by Ronald Chesney and Ronald Wolfe for Hammer Films.

The Magnificent Seven Deadly Sins: The Magnificent Seven Deadly Sins is a 1971 British comedy film directed and produced by Graham Stark.  Its title is a conflation of "The Magnificent Seven" and the seven deadly sins.  It comprises a sequence of seven sketches, each representing a sin and written by an array of British comedy-writing talent.  The sketches are linked by animation sequences.  The music score is by British jazz musician Roy Budd, cinematography by Harvey Harrison and editing by Rod Nelson-Keys and Roy Piper.  It was produced by Tigon Pictures and distributed in the U.K. by Tigon Film Distributors Ltd..

On the Buses (film): On the Buses is a 1971 British comedy film directed by Harry Booth and starring Reg Varney and Doris Hare.  The film is the first spin-off film from the TV sitcom "On the Buses" and was followed by two further films "Mutiny on the Buses" (1972) and "Holiday on the Buses" (1973).  The films are set within a slightly different canon from the TV series; Stan and Jack work for a different bus company (Town & District instead of Luxton & District), and the three films form a loose story arc where Arthur and Olive become parents (despite their apparently sexless marriage).

Supporting paragraphs: Geoff Unwin On the Buses (film)
Answer: Geoff Unwin