Damian's favourite book is called "Six O'Clock Saints". Popular in the UK in the 1950s, it is surprising that any parent would give a copy to their child, as the screenwriter Frank Cottrell Boyce points out at 03:08 in the DVD commentary, since it contains all the gruesome stories that Damian tells in class, plus many more. Its inclusion is a sort of homage to Martin Scorsese, who, according to Boyce, has cited it in interviews as one of his favorite books growing up and that it gave him a wider understanding of the human experience than had been revealed to him as a child. Roger Ebert's 18 March 2005 review of the film, mentions that Boyce "got the inspiration for the screenplay from an interview in which Martin Scorsese said he was reading the lives of the saints."
The film was shooting as the book was being written.
As of 2013, this is Danny Boyle's only film without an R rating from the MPAA in the USA. This is no longer true: Yesterday (2019) is rated PG-13.
Danny Boyle and Frank Cottrell Boyce mention at 27:17 in the DVD commentary, that one of the actors who play the martyrs of Uganda claimed to be a descendant of the real martyrs of Uganda of 1881.
The scene between Damien and St. Peter was not in the original screenplay. Director Danny Boyle mentions at 46:03 in the DVD commentary that he suggested Frank Cottrell Boyce re-write the screenplay as a novel to which that scene was then added. When Boyle read the novel, he decided the scene needed to be in the film because of the emphasis that the saints' appearances had gained in rewrites of the original script, so the scene was re-written in script form and shot as a pickup.
Danny Boyle: [Millionaire] At one point, the family is watching Britain's Who Wants to Be a Millionaire (1998) on television. This show, of course, plays a huge role in Boyle's later film, Slumdog Millionaire (2008).