Based on Joseph Conrad's novel "The Secret Agent", this sports a different title, as Sir Alfred Hitchcock's previous movie was called Quatre de l'espionnage (1936), which was based on stories by W. Somerset Maugham.
The first name of Verloc (played by Oscar Homolka) was changed from Adolf to Karl to avoid any Nazi connections.
Graham Greene, a well-known film critic in the 1930s as well as a novelist, was well-known for his intense dislike of the films of Sir Alfred Hitchcock and also for his no less intense admiration of the novels of Joseph Conrad, whose influence on Greene has been often remarked. However, although this Hitchcock film is a very free adaptation of Conrad's novel "The Secret Agent", Greene was, rather surprisingly, full of praise for it and often said it was Hitchcock's best film. Later and more renowned Hitchcock films found Greene once again indifferent, and he emphatically refused to sell the film rights to any of his novels to Hitchcock.
Ted takes Stevie and Mrs. Verloc for a steak at Simpsons In The Strand. This was Sir Alfred Hitchcock's favorite meal at one of his favorite restaurants.
In the Sir Alfred Hitchcock and François Truffaut Interview Book (page 76), Hitchcock revealed that Robert Donat was supposed to play Ted, but Sir Alexander Korda refused to release him. When John Loder was cast as Ted, Hitchcock felt that he wasn't suitable for the role. So Hitchcock was forced to re-write the dialogue during the shooting.
Alfred Hitchcock: As with most of his films, the director makes a cameo appearance. He can be seen at the 08:56 mark, just after the lights come back on in front of the movie theater, looking up towards the sky as he crosses in front of the crowd.