Continuity mistake: At the end of the dress rehearsal, when the policeman looks around the corner, someone's shirt appears on the armrest of Nathe's chair. (01:01:40)
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)
Continuity mistake: When Gaz is trying to cadge £100 of his ex wife at her factory her head is tilted one way on the long shot and the opposite way in the close ups.
Continuity mistake: At the end of the strip performance Guy throws his shirt into the audience. A few seconds later, when the camera is on Dave, he is seen again in the background waving his shirt. (01:22:30)
Continuity mistake: When Gerald's wife throws the gnome on the ground the head jumps away. When the pieces are seen again the head lies together with the rest. (01:06:40)
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.
Answer: It's a sight gag. Dave's essentially stealing the candy, so the alarm goes off. When he crushes it, the alarm stops. It wouldn't really happen, but it's funny that the alarm stops when he removes the candy.
ChiChi