To prepare for the role of Johnny, David Thewlis read Voltaire's Candide, the teachings of Buddha and James Gleick's Chaos, and the holy books the Bible and the Qur'an.
According to David Thewlis, the only serious improvisation filmed was the scene of Johnny meeting and antagonizing the poster man.
The script was largely created by improvisation during 11 weeks of rehearsal before shooting. The script was only 25 pages long.
Mike Leigh first had the idea for the story while a student in Manchester in the early 1960s: "We had a very enlightened teacher who endlessly reminded us that the next total eclipse would be in August 1999. In 1992 the millennium was impending, so I brought that idea to the film."
The uncut shot of Johnny and Brian in silhouette, where Johnny expounds on his convoluted apocalyptic conspiracy theory, was shot in 26 takes, but Mike Leigh ended up using one of the earliest takes, as he felt it was best.