The Next of Kin, also known as Next of Kin, is a 1942 World War II propaganda film produced by Ealing Studios. The film was originally commissioned by the British War Office as a training film to promote the government propaganda message that "Careless talk costs lives". After being taken on by Ealing Studios, the project was expanded and given a successful commercial release. After World War II and up until at least the mid 1960s, services in British Commonwealth countries continued to use The Next of Kin as part of security training.
(Summary from Wikipedia)