Although it is nominally based on the unsuccessful 1940 play "The Peaceful Inn" (which makes no mention of World War II), this film is chiefly inspired by a real incident of the war which had attracted some attention at the time. The Welsh village of Cwmbach had only one bomb dropped on it by the Luftwaffe during the entire course of the war; it fell on a local inn and killed the landlord and his daughter (no-one else). It has never been satisfactorily explained why this incident should have occurred. It had not been part of an air raid; there were none in this remote rural area.
Mervyn Johns and Glynis Johns were real life father and daughter, the same as the characters in the film.
Roland Pertwee (The Prison Governor) was the father of actor Jon Pertwee and grandfather of actor Sean Pertwee.
Something that would be apparent to UK audiences, but perhaps not to international audiences is that "Parkmoor Prison" is a fictional prison with that name being contrived from the names of two well-known British prisons - Parkhurst Prison and Dartmoor Prison.