Robert Donat was originally slated to play Ted Spencer, but a prolonged illness prevented him from playing the role.
Based on Joseph Conrad's novel "The Secret Agent", this sports a different title as Alfred Hitchcock's previous film was called Secret Agent, which was based on stories by W. Somerset Maugham.
Some critics objected to the way Alfred Hitchcock chose to end the sequence involving the delivery of the bomb on the bus. Hitchcock, stung by the criticism, is said to have regretted his decision. Nonetheless, the treatment is faithful to Joseph Conrad's book.
Some erroneous modern sources identify Sara Allgood as the uncredited actress playing the bird shop customer, but she does not appear in this film. The identity of the actress in question is presently unknown.
The film "Bartholomew the Strangler" is fictitious, as is, so it seems, actor Tom McGurth (who is named on the posters outside the movie theatre).