According to BFI Screenonline, the fifteen year old character of Cathy was played by a then thirty year old Kate Hardie, but the IMDb states Hardy was born in 1969, making her around sixteen years when the movie was filmed.
Bob Hoskins was unaware that Michael Caine was in the film until he arrived on set for the first day of shooting. Caine himself had created the ruse while they worked together on Sweet Liberty (1986). He told Hoskins that he had been offered the part but it was too small and he was tired playing villains, even though he had already agreed to take the role.
Mortwell's strip club is actually the famous Raymond RevueBar in London's Soho district. The giant prop hand Mortwell sits in was a famous element of the show, visible in a lot of promotional material for the club. At one point George walks past a poster for the Festival of Erotica, a real show at the RevueBar at the time.
The picture features the Genesis song "In Too Deep" which also features on the band's 1986 smash album "Invisible Touch". The hit tune was written by singer Phil Collins after he was asked to write a song for the film's soundtrack. The song is heard pretty much in its entirety right in the middle of the movie.
The meaning and relevance of this movie's Mona Lisa (1986) title is, according to the film's synopsis publicity, "a film about a song, about a painting, about a woman; about men, and the images they make of women, the stories they need do tell themselves, to keep them mystic, unfathomable, anything but real...".
The title and lyrics of the film's source "Mona Lisa" song sung by Nat 'King' Cole and heard throughout the movie refer to Leonardo Da Vinci's renaissance portrait painting "Mona Lisa", which can be seen on Thomas (Robbie Coltrane)'s refrigerator about ten minutes into the film.
The famous Brighton Jetty is used as a location in the film's third act but there is no long or establishing shot of the enormity of the notable landmark (as in Brighton Rock (2010)), only medium and close shots of the action on it.
The movie got Oscar nominated for the Best Actor Academy Award for Bob Hoskins, who, despite winning very many other Best Actor awards, did not win the Oscar for this film, losing to Paul Newman for The Color of Money (1986). To date [June 2013], Hoskins' performance in the film remains his only ever Oscar nomination for acting.