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.