The dark laugh, the black laugh, is often the cheapest laugh. I think Oliver Stone's bumbling Natural Born Killers was the moment black comedy lost its sanctity and became just another part of the casual jaundice with which we make it through the day.

Just occasionally, though, something will come along to remind what an oddly life-enhancing thrill a proper black comedy can be and British production Sightseers is such a film – joyful, hilarious, despairing, yet almost touching.

Wheatley is a director whose speciality has been taking the sacred British traditions of social realism, ramming them into traditional Friday night entertainment and revelling in the resulting discomfort. In lazy journalese, his career has been a series of Mike Leigh Meets – Down Terrace was Leigh Meets a Guy Ritchie gangster romp, while Kill List was Leigh Meets The Wicker Man.

In those terms, Sightseers is Nuts In May with a body count. Steve (Steve Oram) takes his new love Tina (Alice Lowe) caravanning around various places of interest in Yorkshire, from pencil museums to stone circles. Even knowing what is going to happen, as the film starts, there is just no way that you can see how this pair, with their flat Midlands accents and put-upon air, could be potential spree killers. Yet the casual way they slide into it is oddly convincing.

The cast's profile works perfectly. Oram and Lowe came up with these characters during a decade or so knocking around on the comedy circuit and popping up in support roles on the telly. Lowe can be seen on Sunday nights in Harry and Paul.

Like any serial killer, they are bit-parters who have seized the centre stage.

This style of observational comedy is often praised for its subtlety and refinement, but often that's a code for snobbery. Here the comedy reveals the fear that fuels that snobbery. You laugh at them, it's cruel, but it never lets you off the hook.

Wheatley's direction gives the film a whole other dimension, a wild celebration of the English countryside both in its stark, raw splendour and the timid way in which the natives try to tame it and pacify it with it their camping trips, picnics and National Trust enclaves. It's a strange and terrible ride, one that makes you want to go out and explore this great land of ours while instilling in you such a dread of and loathing for your fellow countrymen that you never want to leave the house again.

SIGHTSEERS (15)

Director: Ben Wheatley

Starring: Alice Lowe, Steve Oram, Eileen Davies, Jonathan Aris, Richard Glover and Monica Dolan

Length: 88 mins

*****