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: When Angel and Danny jump into the skip, you can see the boxes under the rubbish have been placed there specifically. (01:41:00)
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 the officer holding the double barrel shotgun has it broken open to reload it, you can see that the primers have been dimpled, meaning that they've been fired. The rifle is closed up again without the spent shells being replaced. (01:41:10)
Revealing mistake: When Tim Messenger gets the spike dropped on his head you can tell he has been swapped with a CGI look-alike. (00:56:00)
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: When Michael is unconscious in the freezer after the fight with Angel in the supermarket, there is a close-up of his face and you can see his real teeth behind the prosthetic ones.
Revealing mistake: The shot of Nicholas Angel jumping into the skip is a stuntman with a rather vividly dyed wig.
Revealing mistake: When Angel and Danny are getting the pints at the pub, the same clip is used for the fresh pints being handed to Angel and Danny. (00:45:45)
Chosen answer: In the pub Danny demonstrates using a ketchup packet to simulate stabbing himself in the eye. Later in the film he returns Nicholas Angel's notebook, hiding a ketchup packet in it. He stabs the pocket with the notebook, causing the ketchup to leak and simulate blood.