Corrected entry: In the scene where Billy is getting off a train on the London Underground, he gets off a train that was built in 1996 and also the platform shows the protection doors that the Underground only recently (1999) started using - meaning that this station wouldn't have been there when the film is supposed to have taken place.
Corrected entry: When Billy and Michael are outside the snow, they're making a snowman. When Billy's dad and his friends come by, the snowman now has a policeman's hat, but when Billy and Michael were at the snowman, they didn't put a hat on it.
Corrected entry: Billy walks down a street with his friend the girl from the ballet. The girl has a stick that she pulls along the wall. When they separate, Billy crosses the street and the girl stands on the other side, then a police van passes by and and suddenly she's gone.
Corrected entry: Early on there is a scene where Billy is having a wash. He is covered in bruises and scratches, yet this isn't explained by any earlier scenes.