Goya's Disasters of War is a precocious modern masterpiece, a work left by its creator as his final savage bequest to the 19th, 20th and 21st centuries - it was far too anti-clerical and unpatriotic to be published in his lifetime, and the first ever edition came out in 1863, three and a half decades after his death in 1828. From the very start of its public existence, it has been experienced not as a historic but as a contemporary work, its images so urgent and truthful that they function as living, new art. There wasn’t a whole lot of good art coming out of the UK in the nineties. The landscape was dominated by the YBAs – the Young British Artists, mostly graduates of the posh Goldsmiths college, all of them very comfortable with self-promotion and massive quantities of cocaine. Some of the art they made was striking, some of it was at best memorable, but real capital-A art was thin on the ground – unless it was being made by Jake and Dinos Chapman. It's all very sophisticated. The next day I see the images. I think they are brilliant and profound. Oh dear. Somehow, they do not destroy, but find something new in the Disasters of War. The Chapmans use the word "evil" to describe the atmosphere that pervaded their recent ethnographic show; there is a wild sense of evil in what they've done to Goya. The altered prints make you think a serial killer with an addiction to drawing psychotic clown faces has got into the British Museum's prints and drawings room - like the killer in Red Dragon who eats an original Blake.

if baroque marked the start of modernity, tuymans explores the search for authenticity, the political significance of artistic representation, and the emotional turmoil generated by art. the exhibition title ‘sanguine’— a word that signifies the color of blood, but also a violent and vigorous temperament, and a pictorial technique — suggests a multiplicity of perspectives to interpret the exhibited works, in which violence and its simulation, cruelty and dramatization, realism and exaggeration, disgust and wonder, terror and ecstasy coexist. Children who visit the gallery will get some protection from the Chapmans' more grotesque imaginings. "We're scatter-hanging the gallery," explains curator Selina Levinson, "so we can put the most upsetting images higher up." How does Jake feel about this cunning if sanitising hang? "In this case we have been relaxed about it. We have to be respectful of [the gallery's] thoughts about what the public and the trustees will find acceptable."

Of course, the Chapman Brothers didn't intend anything like that. Ready, as ever, with a dense rationalisation, Jake riposted: "Our intention was not in any way to trivialise the Holocaust." Rather, you see, it was a comment on the innate inadequacy of artistic responses to such genocide. "This is an event that's beyond representation. Using toy soldiers is a way of emphasising the impossibility of that. Here are these little figures that are totally incompatible with the pathos they're supposed to support."

Chapman said he hoped visitors would not be distracted by “personality antics” and would focus instead on what had brought him and Dinos to The Disasters of War in the first place – “but, having said that, of course it’s going to be amazing to see”. The brothers' first joint work is also their first tribute to Francisco Goya, an artist that they have continued to reference throughout their careers. This piece is a three-dimensional representation of Goya's etchings of the same name made in miniature using toy soldiers. Goya's etchings depicted the atrocities of war experienced during the Napoleonic invasions of his native Spain in 1808 including gruesome scenes of bayonetting, beheading, torture, and death. Goya's work provided such a powerful polemic, that it could not be exhibited in his lifetime For some critics, this is all a callow waste of energy. It seems pathetic to take the most powerful of all artist-moralists, an artist who needs no apology or explanation and for whom the deadening phrase "old master" seems utterly inappropriate, and make these sterile simulacra, these crass copies. The critic Robert Hughes, who is writing a book on Goya, has dismissed the Chapmans' translations of his images as superficial exercises.Jake cites Freud's Civilisation and Its Discontents. "Freud wrote that primary instincts are driven out of children for the sake of secondary gains. I may want to kill someone who is in my way on a bus, but it's better to ask them politely to move aside. Politeness gives me a secondary gain. That's what civilisation is like." So, in his art, is he trying to point out that beneath the veneer of civilisation we're all seething ids and repressed psychotics? "I don't think artists can do anything. An artist can only add shit to shit. Dinos once said, 'Our art is potty-training for adults.' He got that about right." The Chapman brothers are trying to help grown-ups be more civilised? "We're not here to help," he giggles. "We certainly don't care about moral instruction. Our interest in morality is not in being moralists, but in how morality works as a functional pacifier." The original watercolor, painted by Adolf Hitler, shows a picturesque scene of civic architecture and is thought to have been produced in the years between 1908 and 1914 when he tried to forge a career as an artist, with little success. The work has been embellished by the Chapman brothers who added the sun, clouds, and brightly colored sunbeams that fill the sky. This is one of 13 watercolors by Hitler that they treated in this way in a bid to "prettify" them. Such an appropriation of a known artist's work is nothing new. In 1953, Robert Rauschenberg removed every trace from a crayon, pencil and charcoal sketch to produce Erased de Kooning Drawing. In doing so, he explored how far one could push an object from its origins and still have it retain its power. He took the work of one of his idols and literally erased it in a way that questioned whether art could be created through the act of destruction. With this act, Performance Art was born, and here the Chapmans do the same, reframing Goya's etchings for a contemporary audience. In altering the work of another artist, the brothers are realizing the destructive element that they believe is at the heart of artistic progress. They said: "All works of art are destructive by their nature, because they destroy what precedes them". The connection between making toy soldiers and making mannequins seemed to be the only way to maintain a relationship between found objects or readymade, which we could manipulate … Disasters of War … was made with the intention of detracting from the expressionist qualities of a Goya drawing and trying to find the most neurotic medium possible, which we perceived as models. It gave us a sense of omnipotence to chop these toys up.