Michael Caine writes in his autobiography that Lizabeth Scott was very insecure because, as she said to him, it was her first film in fifteen years.
Mickey's novels and first name is based on pulp writer Mickey Spillane, specifically the novel My Gun is Long, homage to My Gun is Quick.
Spike Milligan wrote a letter to producer Michael Klinger following a television screening of this movie in 1977. Milligan was considering sending a letter to animal cruelty organizations until he was reassured that a pig hunting scene involved no actual harm to the pigs.
Writer and director Mike Hodges always wanted Mickey Rooney for the role of Preston Gilbert, but did also consider Elisha Cook Jr. for the part for a time until Rooney committed to the movie.