It doesn't fight shy of a truly frightening final twist, which makes it not only bleaker but also more truthful than virtually every other movie in this genre, which all too often is over-populated and under-humanised.
The film's one major fault is that Reilly's character repeatedly acts in ways that serve the plot, but which run contrary to rational human behaviour. By contrast, the shattering downbeat ending is well earned and genuinely shocking.
Instead of Deliverance's deep backwoods hicks we have now backwoods chavs who live a life unscrutinised by cops or anyone. Watkins has consumed all those tabloid hoodie tales and regurgitated a horror.
if it gets people talking about youth violence, class conflict and the gulf of social inequality in Britain, then all the better - and if it does not, at least it will give them a frightening, albeit derivative, ride.