What initially stands out about the Chelsea home of Michel van Rijn is the curious absence of artwork. The lavishly modern, head-high statues of Mary and Joseph either side of front door are just an hors d'oeuvre to the colourful banquet of unlikely objects that litter the abode inside. For someone so imbued with the art industry, the 55-year-old Dutchman - who even claims consanguinity with the artist Rembrandt - is remarkably out of sync from the world whose lurid underbelly he used to run. For having shelved his shady past van Rijn took on the mantle of industry whistle-blower, uncovering the illegal activities of his peers and colleagues by cloak-and-dagger operations and the upkeep of a detailed, accusatory website. Running with the hares, and now hunting with the hounds, van Rijn runs his campaign from a house brimming with plastic ducks, rubber gloves, whoopee cushions and chintzy trinkets: "My own personal manifesto against art," he says.

Having left home at the age of 16, van Rijn - the son of an art collecting dentist father and sculptress mother - made an early fortune forging masterpieces on the black market. Thus began a long career as one of the establishment's most distinguished and irascible crooks. Once responsible for a purported 90 per cent of international art smuggling - "that is a little more credit that I deserve," he dismisses with a flick of the wrist - van Rijn has made, and lost, millions in lucrative underhand dealings. He is a maverick, burlesque, almost Balzacian character: had there been no van Rijn in the art world, surely the industry would have been obliged to invent one.

Renowned for his outrageous pomposity, the heavy-smoking heavyweight is definitely from the eye-for-an-eye school of diplomacy. If you cross van Rijn, expect retribution. During the 1970s, for example, he fell out with premier auction house Sotheby's after they reneged, at the 11th Hour, on a deal to allow his legitimate company to represent them in Japan, the rising sun of the art collecting modern world. Seeking reprisal, he put together an impressive collection of Avar treasure that he supplied through an intermediary to Sotheby's. According to van Rijn, the London based auctioneers, having failed to carry out the requisite checks on the authenticity and provenance of the collection, duly put the sham 6th Century artefacts up for their first ever catalogue sale. "I called up one minute in advance and told them it was a fake," he revels in revealing. "Ha! The auction was instantly called off. They couldn't afford to sell it or I would have exposed them."

While van Rijn is nostalgic about his former bootlegging days, he is adamant that he came clean at the right moment, once the murky world of art crime was no longer one in which he felt comfortable operating. "The life of an art smuggler used to be like that of a pirate," he recalls wistfully. "You'd go to Armenia, meet a contact, have a few drinks, strike a deal - and you'd do all this in front of a bent KGB officer. But now, there are hardcore criminals. You can get your head blown off." He decided to call it a day in 1987 after being arrested in Marbella and held in a Madrid prison for two and a half months. Extradition to France, whose Gendarmes were investigating his part in a former scam, quickly followed. "I had more extradition requests than a serial killer," he admits, betraying both incredulity and pride. "I was beaten in jail and it taught me a lesson. I realised that being your own judge was dangerous."

"My 20s were a challenge for me," he continues. "I was top of the mountain. I capitalised on people's weaknesses and vulnerabilities, but I didn't have the knowledge that I have today. I was naïve. You think you know more and more until you realise that actually you know nothing. I learnt that the art world had no boundaries, that if you push that little bit further then you quickly cross the border and become a criminal. There's a fine line. Spain was a real wake up call for me." The thought of his 6-year-old daughter seeing him behind bars forced him to rethink his priorities in life.

The transition from art crook to the straight-and-narrow was helped by the police's reluctance to send down a man who could be of great assistance. Even before his Hispanic epiphany, van Rijn the surreptitious smuggler was operating with carte-blanche in many areas in return for plying New Scotland Yard and the FBI with information that would help scupper other undesirable elements of the art world. The illicit art industry is worth an estimated £8 billion a year and is second in wealth only to the drugs industry. In a field where the best criminals are always many steps ahead of the law, tit-for-tat, scratch-my-back tactics are the only way to infiltrate and begin a crackdown.

Despite claiming that his sojourn in prison made him realise that being his own judge was perilous, van Rijn betrays no fear of being the judge of others. Nowadays, he passes his time compiling a website that acts as a mouthpiece, arranging unofficial show-trials for all those who fall foul of his crazed gaze and immeasurable energy. One recent 'victim' is Dr Marion True, the former curator of the Getty Museum, who stands on trial in Italy for her complicity in the theft of Italian sculptures, and whose initial resignation van Rijn helped secure last year.

Unlike many, van Rijn refuses to shy away from attacking the very top of the smuggling food chain - the people who by his very own estimation are sacrosanct due to their capacious pockets and links with influential political personalities. A flippant van Rijn talks freely about these men. One, a Manhattan based billionaire, is putatively behind a complete system of looting archaeological sites in Iraq: "The facts are out there," van Rijn insists, "but he's so rich, he's untouchable." He reels off a list of powerful collectors, dealers and institutions in London's Mayfair Triangle who, he argues, are also complicit in the systematic pilferage of historical sites in ancient Mesopotamia, modern day Iraq.

But van Rijn's principle target is a multimillionaire American gas tycoon with close affiliations with President Bush and with whom he is embroiled in an embittered legal battle in the Swiss courts. Backed up by evidence procured by a renowned investigative documentary maker, van Rijn accuses the American of "feeding his greed for art" in a shady deal which saw an alleged $3.5 million line the pockets of the Hezbollah in the build up to the September 11 attacks. An on-going online witch-hunt on van Rijn's website has resulted in the .com version being banned due to the influence wielded by the unnamed man in question, who is now determined to pull the Dutch-registered version from the web. Although concerned, the self-proclaimed "street-fighter" and "man of action" is seemingly unperturbed. While van Rijn readily admits that the controversial content and aggressive, finger-pointing tone of his website might be "a little avant la lettre", he hastily adds that "someone has to do it because it opens debate. Of course, there are mistakes, but there's a lot of truth too."

His outlook is blunt: "If you do business somewhere like the Middle East then you have to get in bed with local authorities, and therefore you are voluntarily sponsoring Terror. Art smuggling is no longer a victimless crime." It is precisely this solicitude that delivered van Rijn from the dark-side and which now drives him to unmask those heavily involved in the ever-darkening black market. Could it be that van Rijn is developing a conscience lacking in his former looting years, an acknowledgement of the bigger picture? "Before, you would buy art with your heart, not your wallet," he laments. "Nowadays, it's just about money. But art should be something you live with, a part of your life." This, in turn, accounts for the garish décor of his house and his own manifesto against art.

Van Rijn brandishes a mock copy of his forthcoming book - The Fifth Sarcophagus - a first fictional novel after the release of his memoirs Hot Art Cold Cash, which took four years to pass libel laws before surfacing in 1993. A film is in the pipeline, he says with much pleasure while dragging on a cigarette. How wrong would it be to cast the hero as a villain? While some laud van Rijn as a philanthropic modern day Indiana Jones, others pontificate that he's nothing but a hypocrite who would betray anyone to further his own needs. For van Rijn, everything is one big game: he seems to get as much a buzz from tricking dealers as he does doing what is deemed morally right. He is clearly driven by the basic thrill of deception.

Clearly an intelligent man, he entered the underworld of a vast and profitable illegal industry at an early age, made a fortune as a self-made Fagin and seemingly had the sense to say 'enough is enough' once the stakes got too high, unlike his Dickensian double. In the process he duped crime squads, collectors and dealers throughout the planet, playing them off against one another and avoiding a serious jail sentence to boot.

His life is indubitably worthy of a Hollywood production, and yet even now, a supposed family man reduced to helping out the authorities amongst a house inundated with kitsch memorabilia, van Rijn is bent on causing a splash. One certainty is that this tempestuous soul cannot walk away from the world of art and its darker protagonists. But it is a very dangerous game. As an informant, he goes for the jugular; as a writer, his character assassinations are venomous. He is embroiled in a risky business, one maybe more ominous than what went before. In 1997 he was even shot at by a Yugoslav hit man sent by the Turkish thief whose $80 million heist van Rijn thwarted with the help of German and Cypriot police in Munich. This is an indictment for the man who claimed he wanted to leave behind the calamities of a lifestyle that could see him get his head blown off. A live-in bodyguard is now a formality. While van Rijn may well be no longer directing traffic in the art industry, he's certainly sitting in the back seat and waving his arms outside the window, perilously close to passing vehicles.