Jess Conrad has said in interviews that Sidney J. Furie told the "boys" to tear up the script and improvise their dialogue.
The film that the four lads start hassling the patrons in the queue for was a real movie, Adua e le compagne (English title: Hungry for Love) (1960). As seen on the poster within the film, this was an actual X-Rated Italian language arthouse film.
Director Sidney J. Furie was only 29 years old when he made this film.
All the 'boys' were played by actors who were in their mid to late 20's. Dudley Sutton playing 18 year old Stan was 29, Ronald Lacey playing 16 year old Billy was 27, Jess Conrad who was Barney (17) was 26 and Tony Garnett, (Ginger) was 26. All of these actors had good careers with Tony Garnett moving into film production fairly shortly after this film and had a long association with Ken Loach.
Both Ronald Lacey (Billy) and Dudley Sutton (Stan) would go on to appear in the comedy series 'Porridge' (1974-77), although not in the same episodes.