Millionaire sues dealer over 'fake' Van Dyck

As portraits go, it is a masterful piece of royal propaganda. The artist shows an imperious aristocrat exuding the gallantry that led him to offer to replace his cousin, Charles I, on the executioner's scaffold.

Some 365 years later, the painting of James Stuart, the Duke of Lennox, is at the centre of a dispute that has put the reputation of a top London art dealer under the microscope.

An American art collector launched a High Court action yesterday against the Old Bond Street gallery Thomas Agnew & Sons, claiming that he was sold the £1.5m painting under the false pretence that it was by the Flemish master Anthony Van Dyck. Richard Drake, a Texan who has built a gallery on the side of his mansion to house his collection, is demanding a refund after finding the picture may be a copy by a pupil of Van Dyck.

The painting was bought by Mr Drake in June 1998 after his buying agent, based in New Orleans, was told "unequivocally" by Agnews that it was by the portraitist to the House of Stuart, the High Court was told. Lawyers for Mr Drake accuse Agnews of falsely making a "massive profit" of 41 times the original price by selling on the work as a genuine Van Dyck.

Experts agree that Van Dyck's paintings of James Stuart are among the best examples of the painter's talent for conveying the refinement and "integrity" of the 17th-century monarchy. The Duke of Lennox and Richmond was a favoured cousin of Charles I and a prominent figure in the royal court. After his offer to replace Charles on the scaffold in 1649 was rejected he joined the royal party who buried the monarch. He himself died six years later, aged 43.

The canvas was bought by Agnews in 1996 for just £36,000 at a Sotheby's sale of the contents of Ickworth House in Suffolk, the family home of the Marquess of Bristol, who died in 1999 after years of drug abuse.

Experts from Sotheby's listed the painting as being "After Van Dyck", meaning that it had been composed in the artist's London studio "under his eye" and not by the master himself.

But Julian Agnew, director of the 185-year-old London dealership, viewed the painting, completed in about 1636, and decided that the auctioneers had missed a genuine Van Dyck. It is a similar version of three other Van Dyck portraits of the duke that hang in the Metropolitan Museum in New York, the Louvre in Paris and Kenwood House in north London.

The disputed painting was subsequently bought by Mr Drake after Mr Agnew had his opinion confirmed by art historians in France, America and Britain, the High Court was told. Joe Smouha, representing Mr Drake, claimed Agnews, the oldest gallery in England still in family hands, failed to disclose the original attribution by Sotheby's. He said: "This is not a typical dispute about the proper attribution of a painting where a dealer simply sells a painting with the same attribution that he bought it. Here, Agnews, in their enthusiasm for making the massive profit they did by reattributing the painting, made a number of serious misrepresentations.

"There can be no doubt here that Agnews' description of the painting as being by Van Dyck was the fundamental element of the sale upon which Mr Drake relied in deciding that he was willing to pay £1.5m."

An expert valuer is expected to tell the judge, Mr Justice Buckley, that the portrait is worth no more than £100,000 and would fetch about £500,000 if it was genuine. The court was told Mr Drake claims a leading expert on Van Dyck, Oliver Millar, surveyor emeritus of the Queen's pictures, told Mr Agnew after he bought the work that it was "clearly a copy".

Agnews rejects Mr Drake's claims, saying that although it still believes the work to be a genuine Van Dyck, it had stated in its sale catalogue that there was a "conflict of expert opinion" regarding the attribution.

Charles Flint QC, for Agnews, said: "Agnews properly attributed the painting to Van Dyck and made fair disclosure of the conflict of expert opinion. There was no term of the contract that the painting was actually by Van Dyck and no representation to that effect."

The case is expected to last two weeks.