The actor who plays the irate bus driver, Sándor Boros is a Hungarian stunt driver, and it is he who drives the bus during the crash scene. In the DVD featurette Crashing a Coach (2007), director Christopher Smith goes into detail about how the crash scene was staged, and in it, he points out how the Hungarian stunt team were "less concerned with health and safety issues" than British stunt teams. Smith explains that for the crash scene, the stunt coordinator told Boros to drive at 35mph, but Boros felt this wouldn't produce a good enough scene, so he hit the stunt ramp at 50mph, producing a much more spectacular crash than Smith wanted. As it was a one-time only shot, this newly spectacular crash forced a hasty rewriting of the screenplay, as due to the severity of the crash, the characters now needed to be substantially more injured than was originally planned. Smith was also amazed that the only safety equipment Boros used during the scene was a seat belt and a motorcycle helmet. Indeed, during the stunt, Boros was knocked completely unconscious.
The logo for Palisades Defence - more or less a square with one corner missing - is a sly hint at the company's way of doing business: by "cutting corners".
Because Laura Harris had such fun on the set with her fellow cast members, she found that she was often in too good a mood to reach the emotional depths needed for her character when it was time for her to shoot. As such, just prior to filming emotionally draining scenes, she would listen to dark and depressing music, to help her get out of the mirthful mood she was in.
The swimming pool full of fallen leafs that Gordon falls into is actually a few inches deep fountain with a diving-board installed on the side.
The casting process lasted four months because director Christopher Smith wanted the perfect people for the parts.
Toby Stephens wanted to do the movie because he'd never done a horror film before and liked the comedy/horror mix of the project.
Danny Dyer's character is fed grapes by a bevy of robed girls in a similar scene to one in Kubrick's A Clockwork Orange (1971).
A second reference to Stanley Kubrick's Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964) is the ending song, "We'll Meet Again," played at the end of both films. The version played in "Severance" is a hard rock version, however.