In a letter to his employer, the London Evening Standard, the 35 accused him of 'virulent homophobia and misogyny', and said: 'The capital deserves better than his dire mix of sexual and class hypocrisy.'
The letter was triggered by a recent Sewell review of an exhibition of works by women, in which he referred, typically enough, to a female nude 'which would have no appeal even to a purblind lesbian'. Undeterred by the charge of homophobia or misogyny , he dismisses the letter as the result of talk between two of the prime movers, the critic Susan Loppert and radio presenter Natalie Wheen.
The latter, he says, 'has been seething ever since I got her thrown off a television programme last year, which she should never have been on, because she's not an expert on Leonardo. She's a woman who will talk with equal enthusiasm about playing the penny whistle in Peru and Rachel Whiteread's plaster casts: a generalist. As such, she has her uses.'
He seizes any and every opportunity to take potshots at the other signatories (who include Sir Eduardo Paolozzi, Marina Warner, Christopher Frayling and George Melly): 'I'm an art historian by training and inclination, and have been for a very long time,' he says. 'I'm not someone who has just moved into art criticism from playing in jazz bands.'
He delights in relating how he wrote to Sarah Kent, art critic of Time Out, congratulating her on the best piece she'd ever written. It proved to be a spoof.
Sewell's iconcolasm and rudeness have made him predictable enemies. But he also has many admirers, among a public often baffled by piles of bricks and plaster casts of rooms. His pacy, frequently funny reviews in the Standard are probably the most widely read art criticism in Britain. 'I think sincerely of the man - or woman, for that matter - strap-hanging home to Wimbledon, who's read the sports pages and there's nothing else to read but the art pages. It is essential to tackle the topic with either an element of humour or such gusto as will hold the attention of someone at the end of their working day.'
To have written about the increasingly abstruse visual arts for a popular paper for 10 years is no mean feat. Sewell is a voice of the people - but what a voice] Strangulated vowels and precious enunciation, upper-class and effete, delivering his condemnations in the tones of some last-surviving Sitwell.
He didn't go to school until he was 11. It didn't occur to anyone, he says, to send him. His father, an Old Etonian, about whom he is reticent other than to say that he never did anything in the way of proper work, committed suicide before he was born. He is working on a biography of his mother, 'but I am not sure I shall survive the writing. It's very amusing, but very painful. She was terrible.' When she remarried - 'don't ask about that' - his stepfather insisted he go to school, and dragged him round until he found one, Haberdashers', that would take him. He hated it.
He is, he says, or more precisely, screeches, 'a Kensington baby'. He lives now in a magnificent white house full of faded grandeur - books and pictures, old carpets and dogs - close to where he grew up. The whirring, he explains, dates back to 1929, which is perplexing until he starts talking about fuses. His education came in - and from - London: 'I'd be told, 'Here's ten shillings, go to a gallery or the theatre'.'
After school he spent a year studying painting, and learned 'enough to know that, though I could paint, I had nothing to say', and then went into the Army for National Service. I ask if he was an officer, and he cries, 'Of course] Oh, I bet that goes in the article] Shit]'
Then it was the Courtauld (he turned down a place at Oxford to read history), where he was taught by Anthony Blunt, who became a lifelong friend and whom he spirited away when the scandal broke that the Keeper of the Queen's Pictures was a Soviet spy. This brought him to the attention of Tina Brown, then editor of Tatler, who asked him to write something about Blunt. What exactly, I ask, was his relationship with Blunt? 'Playing the clown,' he says.
Sewell had by this time spent 10 years valuing pictures at Christie's, and made a failed attempt to be a dealer. He also failed in his first writing commission, because no one in the art world would talk about Blunt. But Tina Brown was sufficiently amused by his note of apology to offer him a regular job as art critic. Three years on, he decamped to the Standard.
Sewell's archly delivered invective is heartfelt. He believes that the kind of art supported by the Patrons of New Art at the Tate ('affecting not only what is shown at the Tate, but at the Whitechapel, the ICA, Camden Arts Centre, the Hayward Gallery and even the Royal Academy') has such a stranglehold that anyone who wants to show other than neo- conceptualism 'has not the smallest chance of an exhibition'.
'Of course, it may be that traditional art is dead. An art form can be exhausted. But the contemporary curatorial world seems determined on novelty for novelty's sake, so that anything which isn't recognisably a bronze cast or painting on canvas must be good. I see no reason, for example, to support Rachel Whiteread (another signatory of the Standard letter) who, having filled a hot water bottle with plaster of paris, really has said and done everything there is to say and do about interior space. She didn't then need to move on to a plaster cast of a house in Bow or the interior of the Tate Gallery.'
What Sewell really objects to is that 'most neo-conceptual art offers no aesthetic lift. Where is the sensual pleasure, the aesthetic excitement, from a pile of rubbish, compared to a drama by late Titian, or a madonna and child by Bellini? Bill Viola's video show should have been in the local Odeon rather than the Whitechapel. Though it would, I fear, have got short shrift there.'
Sewell is vain - he says he is 103 - and snobbish: he changed his dog's name to Titian 'because I couldn't bear the thought of calling out 'Keegan' in Kensington Gardens'. He is almost absurdly camp, but all he will say about his sexual orientation is that he is 'a very private person. I live alone, and treasure my celibacy.'
He is also an entertaining and refreshing critic. Asked on That's Life recently to consider a picture, he pronounced it rubbish. His fellow guests - a dealer and a critic - were to varying degrees complimentary, in suitably art-appreciating jargon. The picture turned out to have been painted by an elephant.