Wikipedia
Rentadick is a 1972 British comedy film directed by Jim Clark and starring James Booth, Richard Briers, Julie Ege, Ronald Fraser and Donald Sinden. It is a spoof spy/detective picture, involving attempts to protect a new experimental nerve gas.
The original script for the film was written by Graham Chapman and John Cleese, both of Monty Python. However, the producers made so many changes to the duo's material (including commissioning additional material from John Fortune and John Wells) that Chapman and Cleese successfully instigated action to have their names removed from the finished print. This left the film with a very peculiar credit; the only on-screen writing credit for Rentadick is given over to Fortune and Wells, who are explicitly credited only with "additional dialogue". However, the British firm Network Distributing released a DVD in 2007 using a print which still shows the names Cleese and Chapman during the opening titles (frames at 2:00 minutes into the presentation), and use their names in their promotional material.