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However, the judge’s ruling may force auctioneers to review standards of practice in relation to special client relationships.

Although Mr Justice Jack found in Miss Thomson’s favour that Christie’s had misrepresented the £1.75m urns to her prior to selling them to her at auction, and that she was therefore entitled to damages, he was swayed by the special client relationship she had with the auction house, not by the cataloguing itself.

Despite the ruling in favour of Miss Thomson, the judge also decided that the urns were probably 18th century originals and not 19th century copies – the central dispute that persuaded Miss Thomson to launch the action. Damages are expected to be calculated according to the value of the urns on this basis.

The case arose after Miss Thomson, daughter of press baron and art collector Lord Thomson of Fleet, was made aware of doubts over the urns, which she had bought in December 1994 at a showpiece sale of objects from Houghton Hall, the home of the 7th Marquess of Cholmondeley.

The judge summed up the complex arguments at the heart of the ruling as follows:

• Christie’s had not been negligent in cataloguing as they had used an acceptable level of expertise and had reasonably concluded that the urns were Louis XV on the available evidence. He said there was a 70 per cent likelihood that they had been dated correctly.

• Even where catalogue descriptions are given in absolute terms, such as here, “it remains nonetheless an expression of opinion, which may later be shown to be doubtful or wrong. That is the basis on which the market proceeds, and that is generally well understood.”

• Christie’s had given way to temptation to boost the urns when they attributed their design firmly to the celebrated Ennemond-Alexandre Petitot without the necessary information to do so. There was also “not a jot of evidence” for Christie’s to suggest that the urns were designed for the Duke of Parma or one of his courtiers. “These matters all provided a feeling of confidence and certainty about the urns, which was not justified.”

• In light of the above and the special relationship with Ms Thomson, in which Christie’s knew that she relied entirely on their expertise, the auction house had a special duty of care to make her aware of any potential problems or doubts over the firmness of their attribution when they chose to promote the urns to her, clearly in the hope of persuading her to bid on them.

The judge concluded that since Ms Thomson said she wanted to buy only “museum quality” works of art and was a novice in the field “She should have been told that the catalogue inflated what could properly be said about the urns and was likely to give a misleading impression about Christie’s knowledge and the sureness of their judgment.”

Ms Thomson had argued that if she had been aware that there was the slightest question mark over their authenticity, she would never have purchased the urns.

Christie’s, who are considering an appeal against the ruling, said: “The basis of [the] award is that, even though we believed the Houghton urns to be 18th century, and even though they are almost certainly 18th century, we should – because she was a special client – have warned her of the existence of 19th century imitations.

“We find this difficult to understand.”

Commenting on the case, Pierre Valentin, head of the art and cultural assets group at Withers LLP, said that the case had not challenged the status of descriptions in auction catalogues as opinion. If the auctioneer accepts a duty of care to the buyer he must exercise that duty reasonably.

He thought auctioneers would need to review the way they treated special clients. “This decision will encourage auction houses to reconsider how they serve their VIP buyers. They will probably need to redefine what they do for them, and perhaps more importantly, what they do not do,” he said.

He too was puzzled by some aspects of the judgement: “It suggests a double standard. The catalogue is good enough for buyers in general but if you are a VIP buyer, you are entitled to further information. Some people may take issue with that.”