Revealing mistake: When the Sergeant has the shotguns in the backpack on his back, and you see a close up of his face, you can see that the shotguns do not have triggers. On plastic prop rifles, the trigger is usually molded into the trigger guard in the pulled back position, and you can see this on these prop shotguns.
Revealing mistake: After Angel gets shot in the vest, you get a good closeup of his bandoleer of shotgun shells. You can see the gold paint rubbed off on the primer side of the cartridges, revealing the red plastic underneath. You can also see that the end of the round either just has paper stuffed into it or is completely empty. A real shotgun round will have a brass cap/primer and the end will either be folded completely over (like the shutter of a camera) or show a rifled slug inside. (01:37:20)
Revealing mistake: When Nicholas and Danny discover the firearms collection and the sea mine at Webley's farm, they end up running from the barn along with PC Walker (and Saxon) who run to the right of screen, and Webley himself, who runs to the left of screen. Immediately after Webley disappears off-screen to the left, his shotgun barrel swings back into shot. The barrel then drops out of sight behind a low grey structure only a few metres from the door of the barn containing the sea mine, putting Webley on the side of the structure facing the barn. Presumably done to allow the 65-year-old David Bradley, playing Webley, to run only a short distance. (00:42:05)
Revealing mistake: After Angel leaves Skinner's office to confront the shoplifter, (before Angel arrives next to him at the shelves) the shoplifter isn't putting any items into his pockets - he's merely miming the gesture.