I was under the impression that the school was assaulted by Chimpanzees that escaped from the local zoo.

the film was shot on location. The security guards office in the film is the security guards office in real life.

I agree. Also the fact no schools in the uk have security guards.

Chavs are animals and always hunt in packs

He tells them there's been a murder, but not that there are violent people on the premises. "There's been a murder" can mean any number of things. In Britain, police officers are routinely unarmed (except for CS spray and batons). Unless specifically told that there were armed individuals on the premises, it would be normal police policy to send an ordinary unarmed double-crewed unit as a first response. They do, however, take it seriously. The police car turns up with its blues and twos (flashing lights and sirens) on. This means that the controller has authorised an "immediate" response, the highest response classification, only authorised for 999 calls that are considered to be genuine and in need of immediate attention. What they probably wouldn't have done in real life, however, is split up.

Ahh, good point.
It's a shame though, could've been a lot better, especially if the school was say, in a remote area, like a small village on an island or something
Either way, good replies, thanks

I was more under the impression that the police weren't sent via the dads call, but via the security guards call. He was told by the head mistress to call if the guy came back on the premises.
That's why I thought as soon as the police got there the female officer said 'I'll see if I can find the waste of space security guard' because he's the one who made the call.

The film wasn't that great, I agree, and as you say could have been a pretty decent movie if handled properly.
However, I think you missed a couple of points. The father was a habitual waster of police time (in the eyes of the police). They knew exactly who he was and had stopped taking him seriously - the classic "cry wolf" situation. Thus, the 2 police officers who did attend believed that this was a routine incident and this was the reason that they were not armed.