SA80's are used by the British Army team during the training exercise at the start of the film, with military blank adapters and SUSAT sights attached. They are later ditched when the team discover the dead Special Ops team, as they would be useless against a real threat.
The Browning Hi-Power is used many times throughout the film, first by Captain Ryan (Liam Cunningham) during Private Coopers (Kevin McKidd) Special Ops training, then by Sgt. Wells (Sean Pertwee) during the attack on the farmhouse, and finally by Pvt. Cooper to kill Ryan in his werewolf form.
On an interesting note, during Cooper's training, Ryan's Browning doesn't have a magazine in the gun yet he manages to chamber a round then shoot a dog in the head and not have the slide lock back.
If there's no mag in the gun, then of course the slide won't lock back. The magazine has to be in the gun for that to happen. -MT2008
A Heckler & Koch SR9(T) with the scope removed and a 20-round magazine is used by Private "Spoon" Witherspoon (Darren Morfitt) and then by Private. Terry Milburn (Leslie Simpson) after swapping his MP5A2 for it. After Terry is taken and killed by the werewolves this weapon is not seen again throughout the rest of the film, although he was not shown holding it when taken. The rifle used in the movie had difficulty handling blanks and the bolt had to be manually cycled occasionally. The reason for the scope removed and the 20 round magazine is most likely because the SR9 is supposed to be a stand in for a H&k G3A3.
A Mossberg 500 shotgun is taken from the Special Ops camp and is used by Pvt. Joe Kirkley (Chris Robson) throughout the farmhouse attack and escape from the forest. Many times throughout the film it is shown firing way more rounds than the real gun can hold (in the typical action movie style).
Used by the team to repel the werewolves. They are not seen taken from the Special Forces camp, so it's possible they could have been taken with the team for the training exercise.
