This movie made a star of Julie Christie, even though she's only in it for a total of twelve minutes.
The audience's first introduction to the character of Liz was shot on the street, verite style. More often than not, the turned heads of the passersby are genuine, as director John Schlesinger filmed their reactions to Julie Christie.
Director John Schlesinger chose Sir Tom Courtenay over Albert Finney, who had originated the part of Billy Liar on-stage, mainly because Courtenay was a less physically imposing figure than Finney, and therefore more believable as a dreamer.
Considering this movie's uses of "pissed", "bastard", and numerous "bloody"s, it was passed with an "A" (now PG) cinema certificate by the BBFC after the removal of one line of dialogue. This was "What you wanted me to do that night", and was said by Liz (Julie Christie) to Billy (Sir Tom Courtenay) during their walk in the park. The line was later restored in all video and DVD releases.
Keith Waterhouse wrote the novel "Billy Liar" inspired by the cartoon story "Walter Mitty" by James Thurber.