He worked as a production assistant at Hammer Films. His duties
included assistant director, second unit director and production
manager. For an upcoming project, the head of Hammer suggested that
Sangster try his hand at writing; if he liked Sangster's script, Hammer
would buy it. This began his career as a writer, the
profession he is best known for. His early scripts were not only for
Hammer, but some of Hammer's competitors as well.