Come all ye unfaithful

The Brothers grim are running late. They eventually amble into an East End pub, bestubbled and bobble-hatted, and apologise, saying that they are not feeling their best. Dinos has a hangover, and Jake, who hasn't, has evidently decided to come out in sympathy. Coffee and Coke are called for, and the Chapmans sit down under a framed photograph of Gilbert and George - apt, because the Chapmans began their career working under Gilbert and George, before superseding them as BritArt's most famous duo.

The Brothers grim are running late. They eventually amble into an East End pub, bestubbled and bobble-hatted, and apologise, saying that they are not feeling their best. Dinos has a hangover, and Jake, who hasn't, has evidently decided to come out in sympathy. Coffee and Coke are called for, and the Chapmans sit down under a framed photograph of Gilbert and George - apt, because the Chapmans began their career working under Gilbert and George, before superseding them as BritArt's most famous duo.

In the YBA firmament, Jake and Dinos Chapman enjoy a celebrity status matched by only Damien Hirst and Tracey Emin, their fame and notoriety keeping them in the headlines - and in the money. Charles Saatchi spent £500,000 on their Hell tableau of miniature soldiers maiming and mutilating each other, and a further £1m on the Chapman Family Collection of mock-tribal totems mixed with McDonald's logos.

Best known for their freakish mannequins of children with adult genitalia sprouting from their faces, the Chapmans tend to speak like SWP-supporting students. Jake, the younger, taller and more voluble, is given to ranting about their "complex critical discourse", the failings of our "liberal progressive middle-class bourgeoisie" and the dangers of modern art being subsumed by "the mass state apparatus". But they love being well paid. Ask Dinos, for example, if his children like their dad's work and he retorts glibly: "They like the toys it gives them."

Jake, meanwhile, almost explodes with indignation at my suggestion that the recent Pharmacy auction, when the fixtures and fittings from a failed restaurant were bought for an astounding £11m - simply because Damien Hirst had been one of the owners - was an illustration of money for old rope. "It's not!" he practically yells. In case you've forgotten, someone was crazy enough to buy a pair of martini glasses for £4,800 (original estimate: £50-£70) and someone else with more money than sense paid almost £2,000 for a salt cellar and pepper pot. "Celebrity is tied into the objects," says Jake wearily, as if explaining something to a child. "It's not something you can divest from anything that Damien does or anything that Picasso did. It's actually part of the job. It is a function of Damien Hirst that he will turn things into money." Dinos picks up a small packet of sugar from the table. "It's about scarcity," he says, studying the brown sachet with intent. "This is worth nothing. But if we sign it... suddenly it's worth something because it's the only one."

I'm tempted to hand him my pen, but think better of it. After all, we're here not to talk about money but to discuss their latest job: curating a music festival with the Chapmanesque title of The Nightmare Before Christmas. Taking place in deepest winter at a Pontins holiday camp in Sussex, it's a seasonal offshoot of All Tomorrow's Parties, a festival devoted to the kind of alternative bands that won't ever get invited on Top of the Pops. Their line-up ranges from Mercury Rev and Aphex Twin to Peaches and The Fall. They're the best-known acts. There are many more obscure ones with names such as Shellac, Quinoline Yellow and Comets On Fire. Topping the bill is a reunion of the original 1970s line-up of Throbbing Gristle, the post-punk pioneers of "industrial" (for which read "unlistenable") music led by the performance artist Genesis P-Orridge. In their heyday, when a Tory MP denounced them as "wreckers of civilisation", they used to cut themselves onstage and throw their blood at the audience, while blinding them with white light and deafening them with high-volume high-frequency sounds. It seems unlikely they'll be including a rendition of "White Christmas" in their set.

The Chapmans won't be performing themselves, although Jake once played guitar in a punk band called Carnage (an early hint of the themes that would later inform his artwork) and even got as far as releasing an EP. "It was fucking awful," he adds, ever eager to develop the critical discourse. Dinos, too, has a musical bent. He enjoys fiddling about in his basement with electronic equipment but has yet to go public. "I just twiddle, making unpleasant noises," he shrugs sheepishly. "I keep being bullied by Jake to come out and perform but I'm not going to do it. I'm not ready... I haven't finished sewing all the sequins on to my frock."

The brothers have, however, did have some unusual ideas for the festival line-up, which might have brought it a higher media profile had they come to fruition. "We wanted to have Gareth Gates," says Jake enthusiastically. "I was going to project myself on a giant video screen behind him, relaying his lyrics in sign language. And I wanted to get Rik Waller, the fat one from Pop Idol, to dance alongside him on a set of elephant-sized scales, and see if he could sweat down to a normal size." "Perhaps," adds Dinos, an idea emerging through his hangover haze, "we could have had Jarvis Cocker on another set of scales, eating cream buns until they both reached the same size and the scales began to balance?" Bizarrely, at least part of this idea - the bit about inviting Gareth Gates - got as far as an official approach to the singer's management, where it was met with predictable derision: "They said: 'Are you taking the piss?' and put down the phone." Undaunted, Jake came up with a new idea. "I'd like to invite church gospel choirs to sing and not tell them there would be a death-metal band onstage at the same time. It would be like a rock opera. We could get them all pitchforks... "

In the meantime, the Chapmans are busy diversifying. In addition to their musical enterprise, they are making a horror film for Film Four and recreating a new version of Hell after its destruction in a warehouse fire in May that incinerated many of BritArt's best known works, including Tracey Chapman's tent with the names of everyone she had ever slept with ( Everyone I Have Ever Slept With 1963-1995). A national newspaper thoughtfully bought her a new one at a camping supplies shop and had it embroidered with the same names as before, in exactly the same style. Their replica, they reported, had taken a single day to complete and cost them just £67.50 - a snip compared with the £40,000 paid by Saatchi for the original. "It's quite stupid of people to weigh up works of art simply by their degree of craft, because things have more value than their intrinsic material value," sighs Jake. "Like stocks and shares. Or money itself - a piece of paper that has a drawing on it."

There are plenty of people who feel that the Chapmans' own work is absurdly over-valued, although quite why that should concern anyone except Charles Saatchi and rival collectors is less clear. It's become a national obsession to look at modern art and query its value - artistic and commercial. Yet the Chapmans' chief concern is that we've become a bit too accepting of it all. Jake bemoans the days when you would walk into the Tate and see a pile of bricks and be affronted by their very presence in an art gallery. "We've long since lost that thing where people used to go and see the Carl Andre bricks and say: 'What the fuck is that?'" he says. "That's suddenly become not a very sophisticated way of looking at art, but only because there's been a sophistication of what's expected about people's reactions. Now we have the idea that middle-class liberal progressive people will go in there and automatically believe that if there's an object in there it is (a) beautiful, (b) has some idealistic proposition about the world, and (c) is not open to critical examination. So why is it there?" That, presumably, is why the Chapmans' work sets out to shock us into a reaction, whether positive or negative, by virtue of its extremism. But no. "I don't think our work is extreme," declares Dinos, by now slowly returning to life. "It's very very benign. People don't look at our work and scream and run away."

You probably wouldn't want to take children to see them, either. "Well, it's not for children, is it?" Jake says severely. "To say it is would be like saying quantum mechanics is for kids - no, it's not. Our aspirations, our ambitions for what we do, are for a severely complex critical discourse that has a critical domain, an engagement with serious ideas." Dinos, perhaps in an effort to prick his brother's pomposity, adds with an easy logic: "Children have their own books, they have their own TV programmes. They don't have to have our books and our TV programmes."

But surely, I suggest stupidly, a child's reaction to art can offer us an alternative response, one unencumbered by our own prejudices and all the other baggage we carry into a gallery from our knowledge of art history and culture. "No, that's an awful awful thing to say," Jake retorts with surprising vehemence. "That notion of naivety, that idea that a child is some sort of mediated innocent view of the world. That is an awful idea, because children are not. They're complex, they're fucked-up, they're sexualised, they're all sorts of things. And the contemporary idea that children are somehow ciphers for this kind of idealistic view of the world... well, they're not."

Crikey, that idea has clearly struck a nerve. Suddenly those sculptures of children disfigured by sexual organs are starting to make sense. But still, I wonder, would the Chapmans take their own children to see their work? "I would," says Jake, who doesn't have any. "But I would be very circumspect about what they would get from it. This faux-naif idea that a child is an amazingly uncontaminated mind that can somehow look at art in a way that adults can't... well I think it's the other way round. I think it's much more interesting to be contaminated."

Dinos, who has two children, aged 12 and 10, doesn't often take them to look at art. "They're not particularly interested in art galleries. If I give them the choice between Alton Towers and Tate Modern I think Alton Towers wins hands down. If I'm taking the kids for a pleasurable day out, I won't take them to galleries; if I want to educate them or grind into them that this is good for them, then I will take them to galleries."

Listening later to a transcript of our time together, it seems less like a conversation than a performance. I'm struck by the contrast between the Chapmans in person - passionate, clever, angry, funny - and their art, with its rigorous avoidance of an aesthetic, its denial of expectations, its refusal to entertain. And then the penny drops. Perhaps that's the whole point. Perhaps we've been looking for meaning in the wrong place. Like their conceptual colleagues, they are the concept, and their greatest piece of art.

The Nightmare Before Christmas, curated by Jake and Dinos Chapman, Camber Sands Holiday Centre, East Sussex ( www.atpfestival.com) 3 to 5 December