Mike Higgins on an exhibition that highlights the art of the ersatz, the sham and the totally fraudulent
Name one painting you're sure isn't fake. The "Mona Lisa", right? Wrong. In 1911, La Gioconda was pinched from the Louvre. She was returned a year later but certain figures still claim that a counterfeit portrait was knocked up in the meantime and substituted for the real thing. Even now, it's claimed by some that one of every two objects sold on the art market is, to some extent, faked. What better time then for "Fake! By Design - The Theft of Intellectual Property". The exhibition, organised by the London solicitors, Collyer-Bristow, features a range of counterfeit art and consumer goods, from Nike trainers to Picasso imitations, which, to the untrained eye, appear to be the genuine article.

Manufacturers employ armies of lawyers to prevent rivals ripping off their valuable brand names, but consumer tests have repeatedly proved that we're far less able to judge the quality of a product stripped of its all-important brand name. It may walk like a duck and quack like a duck, but it ain't necessarily a duck. For all its high-minded high falutin', the art world racks itself with a similar question of authenticity. But just what is a fake, exactly?

On the face of it, the Collyer-Bristow office gallery has an impressive collection. Grunewald's "Stuppach Madonna" (see pic) squares up to a pair of Velazquez portraits, an Ingres drawing vies with a painting by Picasso and a de Lempicka sits alongside a Warhol. David Pearce, Sam Fox and Francesca Balestra Dimottolla are some of the less illustrious names behind these masterpieces, however, and all but one have declared their work bona fide fakes. The exception is the late Eric Hebborn, represented here by a number of fake Rembrandt drawings.

One particular forgery in the exhibition typifies Hebborn's opportunism (not to mention those other infamous forgers Tom Keating and Hans van Meegeren, the subject of an forthcoming biopic) and serves to illustrate the vexed question of authenticity that blights the art world. The notoriously successful Hebborn (in whose 1996 death some see the work of shady art interests) decided to forge the Dutch old master's drawing upon reading that it had been stolen (18 years since its inception, the Rembrandt Research Project has cut the number of works attributed to Rembrandt by over half) . He eventually sold on a fake which he created with the International Herald Tribune's photograph of the stolen work as his only source. Until his exposure in 1978, such renowned institutions as the British Museum, Washington's National Gallery, The Pierpont Morgan Gallery in New York and the National Museum in Copenhagen proudly hung over 1,000 of Hebborn's "originals".

Hebborn always insisted that his own fraudulence merely exposed a wider duplicity in the art market.

"He wanted to prove that it was the experts who were the fakers," says Alice Beckett, author of Fakes, Forgery and the Art World. In the cut- throat market place, reckons Beckett, dealers are unlikely to err on the side of caution when considering the questionable authenticity of an apparent original. "If they can sell a fake as the real thing without any problems then it's in their interests financially to do so."

Combined with the ignorance (some might say dishonesty) of the dealers, the willingness of forgers to slake the volatile art market's thirst for "discoveries" brings cries of "fake!" all too frequently. In 1997, London auctioneers were rocked by the forged antiquities scandal, and this year brought allegations that Van Gogh's final "Sunflowers", sold for pounds 24m in 1987, was a fake. In the end, the discovery of a humble letter was accepted as proof of the painting's authenticity: a judgement, of course, which subordinates any integrity of the work itself to its humble provenance (the hardest part of a work to forge is its documentation). Buyers can also dupe themselves, according to Beckett: "If someone's desperate to own a Picasso and you put a painting in front of them that's vaguely like a Picasso, they're three-quarters of the way to believing it's an `original'."

In many cases, our craving for authenticity also runs contrary to the working methods of many of the artists themselves. From the Renaissance to Henry Moore, painters and sculptors have been happy to instruct a talented student in their particular style and claim the results as their own. What's more, the most celebrated artists are known to have attempted wholesale forgery. Having failed to sell a Cardinal one of his own sleeping cupids as a rare example of classical Roman statuary, Michelangelo later managed to dispose of the "antique" more successfully.

"No-one knows where it is because it's thought to be ancient Roman," says Beckett. "The point is that it'd be worth much more than it's thought to be because it's actually a Michelangelo."

The civil service know how valuable a fake can be, too. A specialist pasticheur is employed to create imitations of the government's art treasures in order to keep insurance costs down and discourage thieves. Furthermore, the artist responsible for the facsimile of the India Office's Wellington bust, Leo Stevenson, has said that the older the work, the greater the challenge to the forger. In the case of the latest generation of Brit artists, this would appear especially to be true. Much of the conceptual art which currently holds sway abandons all ambitions of virtuosity for a jokey underlying philosophical or moral conceit. What price the forgery of today's art when, in the traditional sense, there's no "art" to copy? Alice Beckett puts it another way: `If the work of art is a rotting tomato, what do you do when it finally collapses on you? Do you put another tomato in its place?"