Do not adjust your set

Easily the funniest sequence in Politico's collection of party political broadcasts is a choice offering from 1987. It depicts a young boy in neat school uniform who is addressing the camera directly with a speech about pollution of the sea. He hasn't got very far into his ecological sermon before several kilos of soot descend from the top of the frame, avalanching off his cherubic head to form small drifts on his shoulders and the pleats of his shirt. The soot is quickly followed by what appears to be the contents of an industrial vacuum cleaner bag. All the while the boy speaks on, pausing only briefly to spit out debris. As he is gamely summing up his case against random dumping at sea, a cloacal brown coil languidly flops onto his blackened hair, followed by a cascade of marine diesel fuel, an oily veil which finally obscures his features entirely.

The Green Party was relatively new to this particular form of broadcasting so can perhaps be forgiven for not grasping all the principles at once. They had understood that the use of children was a major plus - subliminally reminding the electorate of its responsibilities to future generations - but they hadn't realised it wasn't a good idea actually to torture them on screen. Tormenting the audience, on the other hand, is standard practice, whether you do it by means of toxically pure concentrations of caring compassion or by stratagems that would be better suited to assisting children with learning disabilities.

In the early days there was a kind of innocence to the form, with most broadcasts opting for the clunking informality so accurately captured in Harry Enfield's Cholmondely-Warner information films. "Hullo Mrs Philpott!" says a Tory speaker brightly in a Conservative broadcast of 1953, before a brutal cutaway gives you Mrs Philpott herself, five-foot six of homebody stereotype, smiling away as if her pension depended on it.

It doesn't take long for the delivery to get a little more sophisticated, though; by 1959 an unimaginably youthful Tony Benn is eagerly inviting viewers to "Labour's TV and Radio Operations room", a kind of prototype Millbank in which Christopher Mayhew served as a one-man instant-response generator. These days the job is done by Excalibur, the Labour party's super-computer, but some things haven't changed. "Of course, politics is not a matter of personalities", concludes Benn, "it's a matter of ishoos."

The ishoos, of course, are complicated - which leads to the political broadcast's most abiding vice - insult by explanation. "Look at France", invites the voice-over to a 1979 Conservative election broadcast, and the camera cuts helpfully to a man in stripy T-shirt, beret and a moustache, cackling Gallicly as he waves the wad of francs his country's free-market policies have secured him. Oh, that France! By April 1986 the Conservatives were in office and had changed to a motoring theme, so France became a clapped out old Renault, being overtaken by the souped-up British economy (licence plate TOR 1E).

Nobody seems exempt from this tendency to treat the audience as if they have learning difficulties: "The model of British politics has been the seesaw," explained John Cleese in 1986, with the exasperated disbelief which was the mark of his party political broadcasts (PPBs). And just in case we had difficulty grasping this challenging concept, he walked over to a small wooden model of a see-saw, complete with little Labour and Tory puppets.

"There's a serious point to all this flora," said Glenda Jackson, speaking to us from a plant-filled conservatory. We suspected there might be, of course, and we realised what it was when Glenda squashed a tray of plucky British seedlings with an ornamental Bonsai tree, complete with rising sun flag. By the time of the last election Britain is out of the potting shed and has taken on the form of bulldog, waddling on arthritic limbs into a lighting effect that the Labour party asks you to believe is a rosy dawn, but which might equally well be twilight.

They aren't all moronic, naturally. Now and then a genuine note of passion or anger penetrates the synthetic outrage and calculation. Even now the 1979 Tory broadcast which cut between a headline reporting Callaghan's "Crisis, what crisis?" statement and montages of uncollected rubbish and pickets' braziers, conveys a sense of furious exasperation at an unsustainable state of affairs.

More recently Kinnock - The Movie, Hugh Hudson's shamelessly lachrymose biography of the Labour leader, can still constrict the throat with its brilliant blend of Brahms and platform rhetoric. But if examples like that mislead you into a false affection for a form that has done us far more harm than good over the years, remember the Natural Law Party's sublime PPB for the last election as a better example of the type. That attempted to persuade us that bouncing cross-legged across a room full of mattresses was "yogic flying" and promised to implement a state of "bubbling bliss" in the nation. A touch more extreme than the usual promises, true, but different in degree only.

`Party Political Broadcasts; The Greatest Hits' is available from Politico's, 8 Artillery Row, London SW1. Tel: 0171-828 0010 priced pounds 19.99