Appearing in this film are no fewer than twenty performers who appeared in at least one of the Sherlock Holmes movies with Basil Rathbone and Nigel Bruce, the latter playing Ramsbottom.
The title comes from the famous line in William Shakespeare's "Hamlet," Act I, Scene III: "This above all, to thine own self be true."
Clive (né Vivian) James chose his name from this character.
In wartime Britain at a station, soldiers and sailors in correct-looking uniforms are getting on and off trains but signs stating track 3 and track 5 and the front of the engine with a lamp in the centre are distinctly American. While the carriage looks British from the side, it looks American when seen from a footbridge and is definitely wider than the engine, unlike British carriages which are the same width as British locos.. The station scene is followed by stock footage of the British engine LNER 4406 passing under a signal gantry which is made out to be the train that Tyrone Power and Joan Fontaine are on. This is a mixture of British stock footage and American studio filming.
Robert Donat, Laurence Olivier and Richard Greene were also considered for the role of Clive Briggs.