Robert Hughes, the world's best-known champion of modern painting and sculpture, is publicly to lay much of the blame for the decline of contemporary art at the door of Damien Hirst. In an uncompromising television essay about art and money that follows next week's controversial London 'clearance' sale of 223 of Hirst's works, the Australian critic will claim they are 'absurd' and 'tacky' commodities.

Hughes's film for Channel 4 argues it is 'a little miracle' that Hirst's 35ft bronze statue, Virgin Mother, could be worth £5m and yet be made by someone 'with so little facility'. Calling Hirst's famous shark in formaldehyde 'the world's most over-rated marine organism', the critic will mount a lengthy attack on the artist for 'functioning like a commercial brand' and make the case that both Hirst and his shark prove that art has lost all meaning separate from its price tag.

Hughes, 70, became well known in Britain with his acclaimed BBC series The Shock of the New in 1980, which made the theories behind modernism in art accessible to a wider audience. But Hughes says he now fears he is a member of the 'last privileged generation' to have visited an art gallery without thinking about the market value of the exhibits.

Hirst's 1991 suspended tiger shark, The Physical Impossibility of Death in the Mind of Someone Living, is, Hughes judges, a 'tacky commodity', even though collector Charles Saatchi sold it for £8m in 2004. 'It is a clever piece of marketing, but as a piece of art it is absurd,' Hughes says. The common defence is that Hirst's work mirrors and subverts modern decadence: 'Not so. It is decadence,' says Hughes.

His harsh verdict on Britain's leading artist is a key part of the new film's argument about the change Hughes has witnessed over 50 years as a New York-based art reviewer. His film, The Mona Lisa Curse, opens with shots of Hirst's diamond skull, For the Love of God, which sold for £50m and is now owned by a consortium. Hughes maintains that all works of art now operate in western culture much as celebrities do. He dates the trend from 1962 when Leonardo da Vinci's Mona Lisa left the Louvre in Paris to go on display in New York. The long queues to see it turned a masterpiece into a mere spectacle, he argues.

The huge sums now regularly paid out by collectors at auctions, placing the lots out of the reach of public galleries, mean that art itself has been redefined. The works, he suggests, are now like film stars, while the galleries have been reduced to the level of the limousines used to convey them to people. 'Art as spectacle loses its meaning,' Hughes warns.

Grayson Perry, the Turner prize-winning potter and artist, welcomed Hughes's intervention this weekend, although he admires some of Hirst's work. 'I always enjoy Robert Hughes's erudite grumpiness,' Perry said. 'We get the art we deserve and Damien is the perfect artist of our times of fluff economies, New Labour and celebrity hype. His skull was brilliant for its brazenness and for the debate it provoked. His work has always been largely about money: I fear his accountant has become his most influential artistic adviser.'

Like Hughes, Perry is concerned about the way the significance of artworks is skewed by the price they attain in the market. 'What has changed is that the market, fuelled by glitzy new wealth, is becoming more powerful than the connoisseurs, museum curators and art academics whose consensus used to decide what was good art. Hedge fund managers and Russian oligarchs are not necessarily known for their sophisticated good taste,' said Perry.

Although Hughes has always been outspoken about BritArt, he has not attacked Hirst so explicitly before. When Hughes was invited to speak at the Royal Academy of Arts dinner four years ago he made only a glancing, disdainful reference to Hirst, saying: 'A string of brush marks on a lace collar in a Velázquez can be as radical as a shark that an Australian caught for a couple of Englishmen some years ago and is now murkily disintegrating in its tank on the other side of the Thames. More radical, actually.'

Ironically, this summer the Royal Academy, the venerable institution in Piccadilly, London, that helped make the names of the BritArt pack with the Sensation show of 1996, is still waiting to hear whether or not Hirst will accept the honour of becoming a Royal Academician - the highest accolade for a working British artist.

Hirst's fellow BritArt stars, Gary Hume and Tracey Emin, are already members of the academy, but the invitation to Hirst to join a club that he once called 'a big, fat and stuffy old pompous institution' is significant. The letter went out to Hirst in the early summer and he has until October to reply.

· 'The Mona Lisa Curse' is to be shown on Channel 4 on 21 September at 6.30pm