"We've basically re-invented the marble" explained one of the Gingell brothers, "We've brought marbles into the 20th century." It isn't easy to imagine exactly what needs improvement in a marble - they've been spherical and hard for over two millennia now, a textbook example of technological stasis. But the Gingell's had an idea of how to strengthen their diminished value in the playground currency markets, by inserting a picture of a Premier League player. Quite a good idea, really, considering what slavish completists children are, and how persistently they can haggle to secure that one missing piece from their collection. Good enough, certainly, to persuade a manufacturer to take up the idea and put some hard figures to the Gingell's fantasies of overnight prosperity. "Like winning the lottery twice a year," said one of the boys near the beginning of the programme, "3.3 million pounds in the first year if it goes big." At this point the profits were still tantalisingly projected - but the confidence of those doing the projecting was very high: "I cannot see it failing... It will not fail... It's too good," said one of the inventors.

You can say this kind of thing in life and not be contradicted by events. Life doesn't care about narrative structure. But in a television documentary, it is a blatant advertisement that some kind of reversal is already rolling down the tracks. As you watched Leon and Vaughan gleefully test driving Jaguars and Porsches, tooting cockily as they drove past the neighbours, you began to fear for them. The next projection was a little dimmer - just a million a year now - and then the dreaming stopped altogether. Everything had gone right but for one small detail - children hadn't gone crazy. Despite Leon and Vaughan's best efforts to kick-start a cult, something else was sucking up the pocket money millions. If Daniel Reed's Modern Times film (BBC2) had ended there it would have been rather deflating - a trite piece of proverbial wisdom ("Don't count your chickens") given a laddish spin. But he had a bounce to finish on, one consistent with the Gingell's unsupported faith in their own bright futures. Vaughan promptly came up with another sure-fire winner for which he needed seed money. They seemed to have picked a banker of unusually optimistic temperament for their first approach: "Obviously you've made a success with Flik-a- ball", he said blithely, "so you've got some credibility." This time, though, the lads weren't pinning all their hopes on one plan - Leon was fantasising about getting a payoff from a brewery after breaking his ankle in a pub carpark, while Vaughan took advantage of the camera to make one last cheeky sales pitch: "If any crisp companies are watching this, we have a cracker for how to make your crisps the biggest seller in the country." The music, as it often is in Reed's films, was excellent: unpredictable and oblique, but always in tune with the images.

Builders from Hell (ITV) sounded dreadful - one of those jerry-built programmes lashed together from dodgy video and other people's bad experiences. But it turned out to be much more soundly constructed than its title suggested - offering some useful information alongside its cowboy stories. Only the middle section seemed pointless - offering a verbal shoot-out between disgruntled client and a doggedly unrepentant builder, in which it was impossible to decide who deserved the presumption of innocence. Builders usually shoulder the blame for the unsealable gap between the ideal and the real, and the blame is not always deserved. But when an errant developer turned up for his interview-ambush in a gleaming Rolls-Royce, it was much easier to decide whose side you were on, and even easier when he began whining. "This just gives a false impression," he complained when a building expert pointed out the staggering inadequacy of the work his firm had done. The victim had rather more serious things to worry about than his image. The floor of his flat was leaning in chunks against the walls while the insurers assessed the cost of repair - half of what the flat cost him in the first place.