Ray Winstone did not hit Phil Daniels with the sock containing the snooker balls despite the scene being done in one take. A crew member laid on the floor and handed Winstone another sock containing ping pong balls. Nevertheless, Daniels claimed it was very sore when Ray whacked him with the sock.
The earlier and original TV version of this movie, Scum (1977), made for the BBC, but banned by them, and was never screened until around fifteen years later in 1991, after the director's death, and part of a season on censorship. The BBC said that they banned it because "There was too much incident packed into too short a time and that they doubted the veracity." So they thought it was pure fiction. But they also said that it "looked too much like a documentary".
The word "Borstal" is a British term for a "youth penitentiary" but it has also been used for "detention centers" and "approved schools". Borstals were for serious offenders and extreme delinquency and were run by the Her Majesty's Prison Service. The meaning of the term "borstal training" was really just another way of saying "court sentence".
The later British prison film Scrubbers (1982), made and released a few year's later, and set in a female British borstal, has widely been considered to be a female version of Scum (1979). Scrubbers (1982) was inspired by the success of Scum (1979) which had been made and released years about three years earlier. Whereas Scum (1979) had male inmates, Scrubbers (1982) instead featured female jailbirds. The two movies are considered companion pieces, Scrubbers (1982) even being referred to as a sequel of sorts to Scum (1979). The two films share a number of same and similar story elements common to both movies.