John Street finds one gong is music to his ears

Earlier this month, the Nationwide Mercury Music Prize - for British or Irish album of the year - was awarded to Antony and the Johnsons for I Am a Bird Now . As well as the cheque for £20,000, the winner saw a reported 900 per cent increase in sales, albeit from a modest base.

The award was discussed on radio and in the press; the ceremony was on television.

There are now, it seems, prizes for everything. (Even in higher education, there are gongs for teaching and journal articles and, of course, The Times Higher will be giving its own awards for the sector in November.) The temptation is to write them all off as cynical exercises in marketing. It is true that when the Mercury was founded in 1992 the record industry saw it as a way of luring lapsed buyers - those people whose adolescent record collections were fossilising on their shelves - back into the shops.

But the prize has become much more than just a clever marketing tool. It has assumed a cultural presence to match the (Man) Booker prize, on which it was modelled and with which it shares a similar media presence. It is, though, different from its literary cousin in interesting ways. The Mercury has had the same chair from the beginning (Simon Frith, a professor of film and television at Stirling University and a well-known rock critic). It has eschewed celebrity panellists and it has avoided gossip columnists. And while the Booker has remained rooted within the conventions of literary fiction, ignoring genre literature, the Mercury has determinedly embraced an extraordinary variety of musics, from classical (Thomas Ades) to jazz (Soweto Kinch), from folk (Norma Waterson) to mainstream rock (U2).

In its embrace of eclecticism, the Mercury has provided a focus for public debates about art. When in 1994 the Mercury preferred the dance music of M People over Britpop Blur, it challenged staid rock conventions. When it gave the prize to Dizzee Rascal in 2003, it celebrated music that was much closer to the avant-garde than easy listening. In doing so, the Mercury has performed a function similar to that of the Whitbread prize when it sparked an argument about the relative merits of J. K. Rowling's Harry Potter series and Seamus Heaney's version of Beowulf .

As well as providing a peg for polemics about art, the Mercury has also opened ears. Besides acknowledging the looming presence of Coldplay (and singling them out from among the other behemoths of rock), it has also given a platform to those who might otherwise never be heard outside their own kitchen - the place where one of this year's nominees, Seth Lakeman, actually recorded his album Kitty Jay .

It is often suggested that all arts prizes are built upon a lie, that it is impossible to judge between such different entities. Even the winners say as much. You cannot, they insist, choose between the Kaiser Chiefs'

smart-alec rock and Polar Bear's freeform jazz. Well, of course you can. We make judgments of this kind all the time, so do those who complain about them.

The Mercury simply makes such choices in public, relatively free of the pressures of advertisers and public relations agencies. It's a public service, and one for which I am entirely grateful as Antony and the Johnsons' song Hope There's Someone embeds itself in my brain.

John Street is a professor of politics at the University of East Anglia.