Continuity mistake: The lads have been caught by the police during the dress rehearsal. Their names are being taken and the clock on the wall in the police station says 11.40 a.m. - it's in daylight. The security videos are brought in and the time on the one they watch is 12:27. (01:02:15 - 01:03:40)
Deliberate mistake: In the very first scene, with Dave, Gaz and Nathan in the abandoned steel works, they only have one girder, but when they're on the car in the middle of the canal, they have two: one balancing on the car roof, and the one Nathe walks across.
Continuity mistake: In the opening scene when the Works band come round the corner, watched by Gaz, Nathan and Dave who are hiding, you see Limper at the back of the band, playing and marching with them. His ginger hair is easily recognisable. Seconds later he's looking up as the security guard. It seems unlikely he'd put his instrument down and leave the band to come and lock the doors. Of course, he appears again in the band later in the film, so we know it was him in the first shot too.