Sent off when they were playing so well: Rivals copied it and listeners had grown to love it, but Radio 5 has only 12 days left. David Runciman, a fan, asks why

Radio 5 finally goes off the air a week next Monday, sacrificed on the altar of news. What did it do to deserve this fate? The BBC may not have an infallible checklist to determine whether a network is performing a public service, but this does not mean there was nothing to go on.

One test is whether the listening figures are rising. Another is whether programmes are being imitated by others. A third is whether the critics are happy. A fourth, perhaps, is whether proposals for change bring people on to the streets. On three of these counts, Radio 5 is still the equal of any of the BBC's networks.

What it was not, inevitably, was the most listened to. Still, it is hard to believe that its founders expected to be judged by overall market share, any more than John Birt, the corporation's director-general, expects BBC 1 to be judged solely by market share in years to come. Radio 5's job was to cobble together what audience it could for its bizarre mix of sports, children's, youth, regional, educational and pop programmes, which is what it did, with increasing success.

Over the past year Radio 5's weekly audience has risen by 600,000 to a respectable 4.3 million (Radio 3 has 3.2 million), while other stations have suffered rather better publicised reverses. It seems likely that some of those who tuned in for the sport, or as refugees from these other stations, have been sticking around - long enough, perhaps, to catch a teen drama, or some bhangra, or one of the magazine shows from Belfast. It is no mean achievement to persuade a football fan to broaden his horizons in this way. It is also an achievement of which the BBC might once have been proud.

What cannot be quantified is the part played in all this by Danny Baker, now haemorrhaging the weekend audience for Radio 1. Baker gave Radio 5 an identity, and a breakfast show to die for. The change in his fortunes has been taken to suggest that he is less funny than he thinks. It does, in fact, indicate that what he does works best in the relative cosiness of the medium-wave ghetto, squeezed in around the sports bulletins. The further Baker gets from Radio 5, the more uncomfortably knowing his brand of humour tends to sound, a process culminating in last year's embarrassing foray into Saturday night television. You can take the boy out of the ghetto, but only if you don't mind him turning his new home into one.

This salutary tale has not prevented others from trying to re-create that Radio 5 magic. Most successful has been Mark Radcliffe, whose late-night slot on Radio 1 makes a virtue of the eclectic format of its Radio 5 progenitor, Hit the North - and also of its style, being a little frayed around the edges. And both Radio 1 and its commercial rivals have had a go at the mildly anarchic style pioneered on 5, which relies heavily on listeners' ironic sensibilities. Only Virgin 1215 has done it anything like justice.

As Radio 5 has found an audience, and imitators, so it has become harder to discover a critic with a bad word to say about it. This is in part because radio critics have nothing to say about sports and pop programmes unless the station is in the news. Radio 5 was checked out when it started and found to be a bit of a mess. Recently its terminal condition has attracted further attention, and the response has been almost elegiac, though the concentration has been on programmes for children and teenagers, some of which may disappear from the BBC's schedules.

Radio 5's sports coverage has been exemplary, as good as anything the BBC does. The best, we are told, will be preserved on the new Radio 5 Live, which will occupy the same medium-wave slot. But Radio 5 is - was - best for its expansive, unhurried style, a quality not readily associated with a news service. Sports stories usually break on cue, while news stories often do not, which is likely to produce clashes in a rolling service devoted to news and sport.

Radio 5's pop and youth shows have been more hit and miss. Michele Stephens, Danny Baker's replacement in the mornings, has been a disappointment. The middle of the day has been consistently unsatisfactory, with regular recourse to relaying forces' radio, phone-ins and quizzes. Still, the advantage of having plenty of filler is that there is also time and space to come up with ideas that work. Radio 5 has experimented with a wide range of broadcasters and found some excellent if unlikely ones: Danny Kelly, editor of Q magazine, Jenny Eclair, comic, and Johnny Vaughan, ironist. It has made the best of home-grown talent, such as John Inverdale, the sports presenter, who now fronts the evening drive-time show.

The secret of innovative pop radio is to find out what people do best and then let them do it. Radio 1's recent mistake has been to decide too soon what ought to work, and then try too hard to make it happen. In trying to sound like Radio 5, it has lost listeners to Radio 5, which has no clear idea of what it should sound like, and has no future anyway.

Radio 5 is to be lost so that Radio 4 can continue on two wavelengths to please a couple of million people who cannot get their radios to work properly, some of whom have complained. Given the absence of public grief over its demise, Radio 5 may not be long missed. And it may be that rolling news is a good idea. In the meantime, it is possible to catch the last few days of what still sounds like a pretty decent impression of public service broadcasting.

The author is a research fellow at Trinity College, Cambridge.