Bob Hoskins' voice was dubbed over by another actor from Wolverhampton out of fear that Americans wouldn't understand his London accent. After Hoskins threatened to sue Jack Gill and British Lion, the dubbing was removed. He was supported by Richard Burton, Sir Alec Guinness, and Warren Beatty.
This film is Pierce Brosnan's feature film debut, his part was supposed to be completely silent, but he improvised one word of dialogue, "Hi".
Harold's plans for the London docks prophetically predicted the creation of Canary Wharf.
Dame Helen Mirren's uncle George Dawson was a London gangster. She recalled that quite a few East End gangsters were extras in the scene where Harold rallies his troops. "I'd be all, 'Did you ever hear of my Uncle George?' 'What, George Dawson?', they'd say. 'Yeah! He went to jail, you know.' "