When Henry Mayhew compiled his great analysis of the Victorian lower depths, London Labour and the London Poor, he used longhand and a team of diligent researchers. These days he would probably tote a camcorder round the streets and the film he would end up with would look very like last night's Cutting Edge (C4)- a study of life on the dog-eared margins of society. Mayhew's brand of lofty human classification is properly out of fashion now; in his first volume he confidently declared that mankind could be divided into two distinct tribes, the wandering and the civilized. But some of his words can still strike an echo: "The nomad," he explained, "is distinguished from the civilized man by his repugnance to regular and continuous labour... by his inability to perceive consequences ever so slightly removed from immediate apprehension... by his passion for stupefying herbs and roots." Not everyone in Dominic Savage's astonishing film fitted that description (I'll come back to the silver-lining later) but substitute "lager" for "roots" and it's a passable account of Steve and Derek, two cowboy builders with a hair-raising attitude to quality control. Lichen is more conscientious in its operations.

The funniest scene in Savage's film showed the results of Steve and Derek's attempts to plaster a bedroom ceiling - a job which they had taken on with their customary breezy confidence but which very quickly got the better of them. They were completing their task with a house-brush ("It's an Artex effect, innit") when the unfortunate householder returned. It wasn't easy to be sure about the provenance of this sequence - putting together the splattered chaos with the presence of a television camera, most people would have at once assumed that Jeremy Beadle was lurking in a nearby wardrobe - but if those involved were acting they did it very convincingly. When the agreed price was inadvertently revealed by the furious client, Steve and Derek promptly started a fight with each other - revealing that their willingness to cheat people didn't observe any boundaries of friendship.

Steve and Derek were admirers of Mrs Thatcher, indeed almost everyone here had taken to heart her dictum about there being no such thing as society. This was a surly crowd of Number Ones, all looking after their own interests with not a thought for those of others. What morality there was, was self-justifying ("You gotta make a bit o' money to put in the kids moufs, anch'yer?") or self-pitying - such as the incorrigible car- thief, whining about the fact that he had been banged up with murderers. Shame seemed to have withered long ago for lack of watering - Alan, a Strangeways alumni who asked no questions about the goods he bought and sold, was happy to be filmed buying a camcorder and video player from three local lads, while Steve and Derek demonstrated how they topped up their meagre earnings by stealing pallets and a wheelbarrow from a builder's yard. Here the camera didn't just provide a witness but an alibi too - the police car that cruised past during the theft presumably assumed that thieves wouldn't be cheeky enough to record their activities on film.

There wasn't much consolation here, but for the presence of Tony, a likeable male stripper who - from what you could see of his act - did not give short measure, and Ian and Karl, two diligent carpet-fitters whose eye for the main chance took the more appealing form of running-up home-made Teletubbie headboards. They were cheated at every turn, by customers who seemed positively outraged when asked to pay for goods they were already wearing out. "Look, you're not in my shoes, lad... you don't know my circumstances," said one woman, adamantly refusing to hand over the pounds 50 she owed, despite the fact that she had it clutched in her hand. The two men persisted with quite amazing placidity in the face of abuse and violence and even seemed to be making some headway in this rather unforgiving business climate. One of them also ran a schoolboys' football team - attempting to offer local children something other than an informal education in the price of second-hand electrical goods. He struck you as a good man, but he'd been hard to find in this company of rogues.