Complex sentence: It was made at Merton Park Studios from a screenplay by Rex Rienits which he based on the script of a television film "Assassin for Hire" which he had written the previous year and was screened by the BBC in September 1950.
Split into simpler sentences: It was made at Merton Park Studios from a screenplay by Rex Rienits. Rienits based on the script on a television film "Assassin for Hire" which was screened by the BBC in September 1950.