When asked what his reactions were to being cast as Ambrose Hilliard, Bill Nighy said: "They were looking for someone to play a chronically self-absorbed actor in his declining years, and they thought of me, which is something that's easier to process on some mornings rather than others."
When Tom Buckley tells Catrin Cole, "Films are like life with the boring bits cut out" he is actually quoting Alfred Hitchcock.
The character Catrin Cole is based upon the Welsh screenwriter and playwright Diana Morgan who worked at Ealing Studios throughout the 1940s. Though much of Morgan's screenwriting was uncredited during that era, she was recognised for her work on the highly regarded propaganda film 48 Horas! (1942).
The film was previously entitled Their Finest Hour and a Half, the name of the novel the film is based on, before it was shortened.
Catrin explains that the real life Starling twins were motivated by the movie to join the ATS but without giving details on what the ATS was. The ATS was the Auxiliary Territorial Service, which was composed of women performing non-combat military service, such as clerical work or telephone operators, that would free up men for combat roles. Queen Elizabeth II (when she was a Princess) and Winston Churchill's eldest daughter also served in the ATS.