Sibling ribaldry

Jake and Dinos Chapman are on a break. They haven't seen or spoken to each other for months. They haven't had a falling out; they just decided to live and work apart for a year and see what art emerged. According to their minders at the White Cube gallery in east London, neither has a clue what the other has been working on; it will be a surprise for them both – and for a sceptical art-critical world – when it's finally unveiled next month.

Jake and Dinos apart! It's unthinkable, like Gilbert leaving George to pursue a "side project" or Jedward chasing their destiny as solo performers. For 20 years, the Anglo-Greek siblings have been at the forefront of the Young British Artist explosion that brought Damien Hirst, Tracey Emin, Sarah Lucas, Marc Quinn, Rachel Whiteread and Chris Ofili national fame.

The Chapmans came on strong, both as artists and as people. Their work was startling and upsetting – child mannequins with penile snouts, dismembered naked figures hung from fibreglass trees, a bonsai Armageddon involving thousands of tiny plastic Nazis – and its makers didn't seem like guys who'd worry about the reaction of sensitive aesthetes. Tall, robust and shaven-headed, they came across as clever young geezers who enjoyed taking the piss out of the art world and would be handy in a scrap, should Brian Sewell, Robert Hughes or any other critics come after them.

Their new show at White Cube, opening on 15 July, is under serious wraps. Nobody from the press is allowed near the brothers' studios so we can't discuss their newest productions. But I was able to throw a few questions their way. Would you say, I asked innocently, that you had similar imaginations? "I'd say," said Jake, "we have different influences which, in terms of our artistic symbiosis, amalgamate and form unconventional aggregates." Come again?

"The fact that there's two of us making the work," said Dinos, "means there can't be a precise point of departure. I make things for one reason and Jake makes things for another reason, so you've already got this thing that's multi-purpose, multi-faceted."

"We're not trying," Jake continued, "to produce a unified sovereignty. We're not interested in the similarities between our interests, but the divergencies. This show will be an exemplar of that. Catastrophic, maybe, but we'll see."

Whose idea was the split, the separation? "Mine," said Jake immediately. Really? "No," he said. "Course it wasn't." There was a silence. "I suspect it'll just be more of the same really," said Jake. "I know what I've made, but I suspect what Dinos has done isn't so different from the work we made before. After 20 years, the work starts to evolve its own components and decide its own momentum.

"The idea is that splitting up this unholy, or holy, alliance, might lead to a more autobiographical output."

"I can't stand autobiographical work," said Dinos. "I mean, who's interested?" Tracey Emin's public appears to be, I said. "It's not interesting. I was talking to my wife this morning and she said, 'It's art therapy'. And it is. It doesn't belong outside her head, I think. Whereas, we're interested in art rather than ourselves."

By now, certain things have become apparent. One is that Jake, when you first encounter him, talks like an art-theory textbook. If I had a quid for every polysyllabic abstraction he used in our first 20 minutes, I'd be a rich man. His elder brother Dinos, by comparison, is more open and conversational, but loves to deny that anything is true about their work. A third thing is that you can't be sure if they're sending you, and themselves, up.

Their first major piece, in 1993, was a three-dimensionalising of Goya's Disasters of War aquatints. Instead of depicting soldiers in the Peninsular War engaging in acts of wanton cruelty, the Chapmans used fibreglass mannequins of pre-teen children with their features distended by penises. Some of the children's limbs were welded together. The tabloid press talked about "paedophile art".

"Lots of things written about the original Goyas were idealistic," said Jake, "they didn't describe the actual work. These images are talked about as depictions of cruelty for a moral aim. But the sublimity of the images works as an indulgence of the violence." You mean Goya's revelling in it? "There are ... libidinal elements. They're sadistically erotic, something that isn't consistent with the moral authority given to the work."

He rejects the tabloids' suggestion that they depicted the sexualising of children. "The point is, if the piece had any correlation to the real world, the penises would've been in the right place. The mannequins were more like Pin-the-Tail-on-the-Donkey, gone wrong. They're about putting wrong things on other wrong things. If you're looking for an artistic meaning, you could call it a kind of genetic Cubism."

"A child is more like a puppy than it is like one of those mannequins," said Dinos, inscrutably. "They're not models of disfigurement or paedophilia, they're sculptures which, if they were alive, they'd be very scary because they could chase you in their trainers."

I know you buy the mannequins, I said, but where did you get the penises? "I sent Jake into Ann Summers," said Dinos. They're not dildoes, I pointed out. They're quite small willies. "Yeah," said Dinos, deadpan, "they were in the children's department."

The wicked brothers returned to Goya in 2003 when they bought a mint set of the original Disasters aquatints and altered them, adding cartoonish faces to the victims and the dying. It was called Insult to Injury. It was a more radical statement than Marcel Duchamp's adding a moustache to a cheap reproduction of Mona Lisa in 1919 and calling it a new work. This was close to vandalism.

"Lots of people say, 'Ooh, sacrilege, they're destroying Goya's prints'," said Dinos. "We say, yeah. What we're going to do is get hold of every set we can. It's our intention to replace every Goya with Jake-and-Dinos-and-Goya. It's malicious piggy-backing. But you could remove every single Goya print and painting and it wouldn't matter. Because he's done his job. He's affected everything around him." He would love, he says, to get his hands on the original Guernica and muck about with it.

They pulled off a coup in May 2008, when they bought 13 banal watercolour landscapes by Adolf Hitler for £115,000 and transformed them, adding smiley faces, rainbows and psychedelic skies, for an exhibition at White Cube called If Hitler Had Been A Hippie, How Happy Would We Be.

Jake experienced a weird moment while painting over one watercolour. "As you mix the paints, you tend to subconsciously model the tip of the brush with your mouth, just to keep it in order. So I had the brush in my mouth, started painting on the painting – and I suddenly wondered if Hitler had done the same..." Oh my God! A molecular exchange of saliva with the dictator! What professional subversive wouldn't relish that?

Three years earlier, they'd presented Hell, a display both epic and miniature of an army of 10,000 tiny Nazi soldiers enduring torture and death in battle. It was shown in nine glass cases arranged in swastika form. Some thought it a moving anti-war statement. The brothers did not. "The amount of people who misunderstand Hell," said Dinos, sadly. "People were crying. Over little bits of plastic this big. The overriding function of that piece is to undermine the notion of the grandiose statement."

I asked about the terrible Momart fire of 2006, when it and other Saatchi artworks were destroyed. Was it very traumatic for them? "We were pissing ourselves laughing," said Dinos. "Think about it – Hell going up in flames. Everyone got very sanctimonious. One guy came up to me, put his hand on my shoulder and said, 'I'm so sorry Hell burnt'. I was suppressing giggles. It was s***. Thank God it burnt."

Their artistic double-act didn't start in the nursery. As both brothers will tell you, they were hardly even friends when young. They were born four years and several miles apart, Dinos in London in 1962, Jake in Cheltenham in 1966, to a British art teacher father and a Greek-Cypriot mother. "We only really met each other when we ended up at the Royal College of Art together," said Dinos. "The conversation started, and we both realised we were more interested in the combination of these ideas we were having, than our own work."

There's one topic on which they agree. "Jake and I don't believe in genius, or in talent," said Dinos. "We believe in application and concentration. Every middle-class Victorian young lady could draw, play piano, write poems, these are all very learnable skills. Now there's people like Tracey, who draws, I think, very badly, and everybody claps their flippers together and says how wonderful. If you believe in genius, you don't have to try very hard." His brother agreed. "I think genius and talent are incredibly unfruitful concepts. They'll get you the first five yards but then you're on your own. It's all about hard work." Do you realise, I said, how much you sound like a Victorian schoolma'am? "It is, I'm afraid," conceded Jake, "a dangerously Protestant thing to say."

You wonder if the Chapman brothers realise how they give themselves away at these moments, as dabblers in mild shock and horror and subversion, with nothing in particular to say, and no serious intent as artists. But they'd doubtless answer by saying of course they have nothing to say, you fool, that's the point. They'll probably reveal, in two months' time, that they didn't split up at all for months, and the new works at White Cube were collaborations (you gullible twit).

They are, I think, genuinely talented artists who like to pull the rug from under anyone who admires or disparages them, then go off and giggle together. What a pair.

"Jake and I only make things that amuse us," said Dinos, as we parted. "Doing something as stupid as art, the only thing you can expect from it is a bit of pleasure. So I make things for Jake and he makes things for me."