COLLECTORS of works by Andy Warhol have been put on guard after one of his pictures, valued at £1.4m, has been written off as virtually worthless.

Despite earlier verdicts that the self-portrait completed in 1965 was authentic, a committee charged with protecting Warhol’s artistic legacy has decided it is not genuine.

The ruling will be watched by the Tate gallery, which has 49 Warhols, and private collectors such as Laurence Graff, the British jeweller who paid nearly £7m for a painting of Elizabeth Taylor.

Other prominent owners of Warhols are Robbie Williams, the singer, and Lord Archer, the novelist.

The Andy Warhol art authentication board dismissed a painting put up for sale by Joe Simon, a film producer, for £1.4m. He had originally bought the work for £120,000 in 1988.

The board, based in New York, became involved when Simon’s would-be buyer asked it to check the painting. It decided the work was not authentic and stamped “denied authentication” on the back. It rejected Simon’s appeal.

The red-coloured Warhol self-portrait is one of 10 painted in 1965 for a party thrown by Richard Ekstract, a magazine publisher. Ekstract has one of the 10, given to him by Warhol. It hangs in his house and he has no doubt of its authenticity.

Simon was infuriated by the board’s decision because previously the painting had been authenticated by the Warhol Foundation and Fred Hughes, Warhol’s business manager and sole executor.

“I bought it as a purchase instead of investing in a house,” said Simon, an American who works most of the time in London. The authentication board does not disclose why it rejects about one in six works presented to it. It declined to discuss Simon’s painting for a BBC1 documentary Andy Warhol: Denied, to be broadcast this Tuesday.

To credit a work as a genuine Warhol, the board is believed to require evidence the artist supervised and oversaw it. Hundreds of his works were inspired rather than executed by the artist. Teams of juniors were employed to carry out his wishes.

“There is no such thing as an authentic Warhol,” said Paul Morrissey, former manager of Warhol’s studio. Ronnie Cutrone, Warhol’s painting assistant, told the programme: “Actually, Andy rarely got involved. He had an ability to let go and say ‘you do it’. It was easy to rip off his paintings and sign for them.”

Sam Green, who curated several Warhol exhibitions, even had “signing authority” from the artist. “I would do his signature. Andy only cared about authorship when it came to selling,” he says.

The Tate says the authentication board has only queried one of its Warhols.

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