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.
At 38:37 in the DVD commentary, Frank Cottrell Boyce says "On the nature of this heist, where the guys rush the train and raid the train and actually it turns out that that's not the robbery, it's just a distraction, just a way of planting someone in that 'house'. You came up with that idea from Northern Ireland." And Danny Boyle responds "That's right. I heard this story about the troops raiding streets in the Falls Road in Belfast. It was just a distraction in order to drop a couple of men in the attics of the houses for a couple of days, out of contact and just simply eavesdropping, and then they would raid the street again and take the men out and nobody knew that they'd been there."
Damian is wearing a red, knit, collarless shirt and denim jacket at 14:24 on the DVD when speaking with St. Clare of Assisi in his cardboard hideaway. After the sports bag of money lands through his roof, he scrambles out in a yellow, knit, collared, school shirt and cloth or nylon jacket.
When they are covering the bedroom wall with pounds at 01:17:29 on the DVD, Dorothy is wearing one of Mum's dresses (disclosed as such in "Duffel and Wallpaper" in the deleted scenes of the DVD). However, the same dress is also used as a curtain for Damian's cardboard fort (shown when "the man" is examining it at 29:20 on the DVD).
The film is set around Christmas in England. Yet shadows are relatively short indicating the time of shooting to be summer. The pupils in the playground are not wearing warm clothing, which they would if it were winter.