RADIO / The last laugh: How to destroy a perfectly good joke. Robert Hanks on Radio 4's killjoys

The way BBC Radio Light Entertainment works is, you assume, something like this: when a new Radio 4 comedy programme is in the pipeline, the producer gets all the brightest young sparks in humorous writing to send in their very best jokes for consideration - quips, one-liners, sharp little fragments of comedy perfection. Then they weed out those that are too rude, too political, too clever. Taking the few that remain, they suggest changes to pull them into line with Radio 4's standards. This one-liner is too quick - tack a bit of explanatory dialogue on the end. That punch line - wouldn't it be even funnier if we put a musical link there? This monologue - yeah, very amusing but wouldn't the laughs be even bigger if the audience had to wait for them? Let's pad it out a bit. Now this joke is very good - a shame to waste it, in fact, so we'll repeat it. It's what we call a running gag . . .

It may not happen like that at all, but it would explain why Radio 4's schedules are dotted with patchy, flabby sketch- based comedies that just miss being as funny as they should be: Lionel Nimrod's Mysterious World, And Now In Colour, A Look Back at the Nineties, The Skivers and, at the moment, Paris, London (Radio 4, Thursday). The first programme in the second series of Paris, London illustrated the sort of thing that can go wrong. One of the opening sketches was about a hospital ward full of casualties of modern life: people who've fractured their spines picking up the Sunday papers, speed bump victims, and a huge influx of injuries. Train crash? No, new gym round the corner.

This is not a bad joke, but it works only because it's snappy. It reached its natural terminus, and the sensible thing would have been to leave it there; instead we got an explanatory note ('80 per cent of our patients are keep-fit novices') and the impact was dissipated.

Then there was a piece about an actress with a sordid personal life who is blackmailed by a magazine; pay up, or see yourself in Goodbye] The joke might have been that Hello]'s cuddly exterior hides this kind of extortion, but the writers didn't want to use the magazine's real name; or it might have been that there is a magazine called Goodbye] which is the diametric opposite of Hello] Who knows?

The Skivers, which finished a week ago, was better - at least it had some distinctive features, such as deadpan surrealist voiceovers by Patrick Allen ('For purposes of identification, I am not a hat'), guest stars from Seventies sitcoms, and a line in jokes about children's television and late Seventies / early Eighties pop that presumably leaves anybody under 25 or over 36 scratching their heads. The interesting thing about it is that - bit of inside information here - Nick Golson, who co-stars and co-writes with Tim De Jongh, was David Baddiel's comedy partner at university; and many felt Golson was the talented one.

But this is by the way: the main point is that both shows reek of writing talent diluted by lacklustre acting and production, and indulgent editing. With On the Hour and Knowing Me, Knowing You departed for television, Radio 4 comedy is no laughing matter.