Jack Hawkins, James Mason and Stewart Granger turned down the role of Melville Farr. Then it was decided to make the character younger and Dirk Bogarde accepted the part.
Although, by the time of this movie, the British police were tending towards leniency in their treatment of homosexual offenders, it would not be until the Sexual Offences Act 1967 (citation 1967 c.60) that homosexuality between consenting males over the age of 21 was decriminalized. Even then, this established an uneven age of consent (16 for heterosexual activity), applied only to England and Wales (Scotland followed in 1980 and Northern Ireland in 1982) and did not apply to the Merchant Navy or the Armed Forces. The Criminal Justice and Public Order Act 1994 reduced the homosexual age of consent to 18 and the Sexual Offences (Amendment) Act 2000 further reduced it to 16, bringing parity with heterosexual activity.
At one point, the character of PH is shown outside a theater showing the musical 'Oliver!' on its billboard. In a later scene, the Police Inspector says that, as police, they cannot be dealing with the "Bill Sikes" of the world all the time. Bill Sikes is the notorious criminal in Charles Dickens' novel 'Oliver Twist' upon which the musical is based.
Due to the film's subject matter the BBFC studied the script before official submission and several lines of anti-homosexual dialogue were removed. Eventually John Trevelyan agreed to pass the film after cuts to 4 lines of dialogue including Melville Farr's confession to his wife of his homosexual urges ("Because I wanted him. I WANTED him!"). Surprisingly 3 of these were rescinded upon appeal, including Farr's legendary admission, and the only cut made to the film was the removal of a line of dialogue referring to an adolescent boy 'making the wrong choice'.
Many performers refused roles in this film because of the subject matter.
The comment about the rage of Caliban is a reference to the character from "The Tempest" by William Shakespeare.
The word "queer" is used in two contexts in this movie. Firstly in "Queer Street" meaning to be in difficulties, particularly financial. Secondly in the whitewash daub on the garage door "FARR IS QUEER" meaning he is gay.
This was the first English language film to use the word "homosexual."