The play being performed at the Walsham Bay Repertory Theatre is "Night Alone", starring Hugo Bale, Molly Lester, John Flaxton and Carol Burns. This was a genuine play from the late-'30s and is an in-joke as, like this film, it was written by Jeffrey Dell.
Most of the action on the coast takes place on the Dungeness peninsula, near Lydd in Kent, UK. The final chase scene is on the shingle of Holmstone-Lydd firing ranges, SW of Lydd, some of which is dotted with dense holly thickets (seen well in the film) forming a distinctive and peculiar maritime vegetation-type which is perhaps unique in the world.
Carol Olver's debut.
The car in which Viner and Molly get a lift is an Austin A90 Atlantic convertible. They were produced from 1949 to 1952 and half the production run was exported, though it flopped commercially in USA.
At one stage William Hartnell's character gives advice to Edward Underdowns's character about forming relationships with witnesses. He says that he was a much older man with experience however Hartnell and Underdown where the same age, both born in 1908. Underdown was also 22 years older than his leading lady.