Random Trivia For This Title:
- The siege at the end of the film showing the police in a gun battle is based on the real life Sidney Street siege which took place on 3 January 1911 in London.
- The film's producer, [?] C.M. Woolf, hated the film and only allowed it to be released as the bottom half of a double bill. Nevertheless, it won rave reviews.
- Peter Lorre's first English language film.
- The title of this film comes from the name of a book written by [?] G.K. Chesterton.
- The crucial cantata for the [?] Albert Hall sequence was composed specifically for the film by Arthur Benjamin, and the same piece was used again in the 1956 remake. When Alfred Hitchcock remade the movie, he offered composer Bernard Herrmann the opportunity to compose a new work for the scene, but Herrmann chose not to, citing an appreciation of Benjamin's original cantata.
- The logo for Gaumont British Pictures is located on a scarf worn by Leslie Banks during the opening scene.
- The dentist scene in this film was originally intended to take place in a barber shop. However, Alfred Hitchcock saw the film I Am a Fugitive from a Chain Gang, in which there is a scene exactly like it, so he changed it to a dentist's office. The film was originally intended to be another film in the Bulldog Drummond series entitled Bulldog Drummond's Baby. However, Alfred Hitchcock and writer Charles Bennett did not get the rights to use the Drummond name.
- When Peter Lorre arrived in Great Britain, his first meeting with a British director was with Alfred Hitchcock. By smiling and laughing as Hitchcock talked, the director was unaware that Lorre had a limited command of the English language. Hitchcock cast him in The Man Who Knew Too Much. Lorre learned much of his part phonetically.
- Apart from the opening and end credits, there is only source music in this film, i.e. music that can be heard by the characters, such as dance music in Switzerland and Wapping, and the Benjamin cantata (with the rest of the concert on the radio). There is no underscoring music at all.