Factual error: About 20 minutes in, the group find a Welsh miners' group in the phone book. The character who is making the call speaks the first two digits of the phone number: "0, 1,..." The movie is set in 1984, when the dialling code for that district was "0639" In that year, "01" was the code for London, not Wales.
Continuity mistake: When the woman stands to sing "Bread and Roses", there is a man in a green shirt with a mustache to her left. The camera pans to other miners. When the camera pans back to the original singer, 20 seconds later, the green shirted, mustachioed man is no longer there.
