Sotheby’s auctioneers are being sued in the High Court over claims of professional negligence arising out of an undervaluation of a painting, now thought to be by Caravaggio.

Lancelot William Thwaytes, former owner of the painting, claims that Sotheby’s wrongly attributed it in 2006 to a follower of Caravaggio rather than to the artist himself, estimating its value to be between £20,000 and £30,000. The late Sir Denis Mahon, who bought the piece for £42,000, later identified the painting as an original Caravaggio worth £10 million.

The claims question Sotheby’s research of the picture, deeming it insufficient prior to valuation. Mr Thwaytes maintains that Sotheby’s should have consulted the correct experts over the authenticity of the piece and subjected the painting to further scientific analysis. He alleges that Sotheby’s were negligent in their advice relating the painting.

Even if Mr Thwaytes is successful in his claims of professional negligence, he will have to prove financial loss. This includes convincing a judge that “on the balance of probabilities” Sir Denis’s authentication of the painting as original is more likely than not to be correct.

Sothebys, for their part, are forcefully challenging the allegations, contending that the work was correctly listed as attributed to a follower of Caravaggio’s and that their experts were “entirely competent” to make this assessment.

Specialists expected to appear supporting the authenticity of the painting include the director of the Vatican museums, Antonio Paolucci, and notedart historian, president of Florence’s Roberto Longhi Foundation and author of several books on Caravaggio, Mina Gregori. Sotheby’s too have enlisted impressive scholarly support to maintain their position, among them Caravaggio scholar, Professor Richard Spear.

In 2010 Christie’s art auctioneers were involved in a similar case. The claimants sold a painting at auction for £8,000 that Christie’s had advised was from “the school of Titian” but probably not by Titian himself. They alleged that Christies’ experts had been negligent in that they failed to research the painting completely when advising on its value. The work was subsequently identified as an authentic Titian, a “lost masterpiece”, and put up for auction at a low reserve price of £4 million (although it failed to sell). The dispute was settled for an undisclosed amount.

A similar case in 1989 involved the under-cataloguing of a ‘sleeper’. In Luxmoore May v Messenger May Baverstock the claimants sued the auctioneers for negligence in failing to research a pair of paintings adequately and undervaluing them at £20-£30. The paintings were subsequently sold at auction for £88,000. At the first instance hearing they were successful but the decision was then overturned by the court of appeal. It was decided that among general practitioners the standard of skill and care allowed for differing views. Moreover, the judgment drew an analogy with medical malpractice law and made a deliberate distinction between what could be expected of the general practitioner and what was to be expected of a specialist. In this case, Sotheby’s, a leading auction house with significant resources, would be expected to research competently. Clearly auction houses have to tread a fine line between all of caution, the risk of litigation, the desire to have a big blockbuster name in their catalogue and keeping their clients happy!