Factual error: When the house explodes, the only survivors were Private Cooper and the dog, who were hiding in the cellar. With an explosion big enough to destroy the house, the cellar would have been destroyed too, if not from the fireball then definitely from the shockwave. (01:35:00)
Factual error: Quite a few of the squad actually hold their weapons in either hand, in other words sometimes they have them left handed (Cooper actually has it left handed throughout). This is seen when they are together, so it is not through flipping of the negative. Apart from the fact that it is highly unlikely they would be skilled enough to be this ambidextrous, the SA80 is almost impossible to safely use this way. The ejecting cartridges would be fired out far to close to the face to be safe - if you look at the weapon in some shots you can see the port through which they are ejected - it is covered with a flap behind the cocking handle on the right hand side of the rifle). (00:20:20)
Other mistake: The werewolves have cut the power to the house, but in half the scenes there is an electrical light source. How is this possible?
Visible crew/equipment: In the scene where Spoon is used as a distraction he jumps out of the bedroom window, when it goes to the werewolf's point of view you can see the set of ladders he had to climb up to get to the "window", (as the house is just 2 walls and scaffolding). This is pointed out in the DVD by one of the producers. (01:07:25)
Continuity mistake: When Joe is complaining about missing the football match and Sgt. Wells says "Yeah, well it's nothing like this at all, is it Joe?", Wells is holding his hand under the front part of the machine gun. When it cuts we can see him resting his hand on top of the front part of the machine gun. (00:08:20)
Continuity mistake: When Cooper locks himself in the bedroom towards the end of the movie and looks for a way out, the wash basin does not sit on its support, a gap can be seen, but the next time it's seen it sits flush with the support. Also Cooper kicks at it rather tentatively actually not making contact a couple of times before a feeble looking touch sends it crashing.
Continuity mistake: In the scene where Ryan tells Cooper to shoot the dog, Ryan pushes the gun parallel to Cooper's chest, the barrel is horizontal. As the camera view changes, the barrel's direction changes, pointing up at a 45 degree angle. The pistol continues to do this 3 or 4 times as the view switches back and forth. (00:03:35)
Factual error: The Agusta A109 helicopter that drops the squad into Scotland carries a incorrect UK military serial. 'XZ2541' is one number too many - UK military serials are two letters, followed by three numbers. Also, at the time of filming the only Agusta A109s on the UK military register were operated by 8 Flt, Army Air Corps and were dedicated to SAS support. (00:07:30)
Other mistake: Near the end of the film when the remaining squaddies are attempting to blow up the barn, Spoony ruptures the tank causing petrol to spill out from underneath the car, then the Sarge lights the trail leading to car. However when Cooper is driving the car into the barn you can see in various shots of the car being driven across the grass towards the barn that there is no petrol spilling from underneath the vehicle, so the trail would have large gaps and the car wouldn't have been able to explode.
Factual error: The British infantry has sections of eight men (1 corporal, 1 lance-corporal, 6 privates), not squads of six men (1 sergeant, 1 corporal, 4 privates).