The guardians of Salvador Dalí’s estate are threatening legal action over a new book by a Belgian former art dealer and self-confessed fraudster, which is being turned into a film starring Al Pacino.

Released in Spain today, the book about the flamboyant Spanish artist is laced with sensational accusations — even for a man who deliberately courted controversy during his lifetime.

In Dalí & I: The Surreal Story, the author Stan Lauryssens alleges that Dalí authorised thousands of forgeries of his own work in his later years to fund his increasingly lavish lifestyle. Up to half of all Dalís are outright fakes, Mr Lauryssens suggests.

He also spices up his story with tales of Dalí's supposed orgies with actresses, sexual exploits with young boys and accuses his wife, Gala, of stealing from Kirk Douglas’s wallet during a 1969 visit.

In Spain, where Dalí is venerated as a national hero, there was widespread anger about the book’s allegations and the author has been dismissed as a fantasist.

“The contents of Dalí & I lack the most minimal credibility,” said the Gala-Salvador Dalí Foundation. “These falsehoods can only be explained as part of a promotional campaign for the book and the film, which will be realised in the complete absence of any historical, artistic or ethical rigour.”

The foundation vowed to take the “necessary legal actions” to defend the artist’s reputation.

In his book, Mr Lauryssens quotes several people who worked closely with Dalí to back his contention that the world’s museums are packed with fake artworks that were only signed by the artist or his representatives.

“Dalí got half a million [dollars] for signing blank sheets,” the artist’s US lawyer, Michael Ward Stout, is quoted as saying. “There came the time when he could sign one ... every two seconds.”

He also quotes the painter Manuel Pujol Baladas as saying that the artist's wife paid him to churn out fake Dalís during his later years. “Gala and Dalí flooded the market with fake Dalís,” he is quoted as saying. “My surrealist paintings are on permanent display in major museums around the world, though they bear the signature of Dalí.”

Though he can hardly match his subject’s storied past, Mr Lauryssens has a richly controversial history and critics have questioned the truthfulness of many statements in his book. He claims to have started out his professional life drilling holes in Emmenthal cheese to sell-on as grated cheese before becoming a rogue journalist, writing up fake interviews with Hollywood film stars for a Belgian weekly magazine.

A fictional interview with Dalí drew the attention of a shady investment group, he says, and soon he was selling real and fake artworks to wealthy people who wished to launder money. After earning a fortune, Mr Lauryssens ended up becoming Dalí’s only neighbour in the village of Cadaqués, in Catalonia, before being imprisoned in Spain for selling forged artworks. He has subsequently reinvented himself as a crime writer.

The author's life is due to reach the big screen next year, courtesy of Andrew Niccol, who wrote and produced The Truman Show and wrote and directed Lord of War. Mr Lauryssens will be played by the Irish actor Cillian Murphy, who has starred in Batman Begins, Cold Mountain and Girl with a Pearl Earring. Pacino is lined up to play Dalí.

In a recent interview with the Spanish newspaper ABC, Mr Lauryssens said that he was overjoyed about the upcoming film. “It's curious,” he said with a grin, “Dalí enriched me once in a completely illegal way, and he has now done it again legally.”

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