Enjoy unlimited access: just £1 for 12 weeks

Subscribe now

The move comes as the judge ordered that Miss Thomson should recover only one third of her costs. In practice, this means that she will recover around £200,000 of the £700,000 she was seeking, say Christie's, who added that the judge's order reflects the fact that significant issues in the case were decided in the auction house's favour.

At the heart of Christie's appeal will be an argument that the judgment was not sound as it was not based on the original claim. Christie's will argue their appeal on several counts, including:

• The judgment was not based on the original claim that Christie's were negligent in dating the urns as 18th century, but on a reformulation of that claim by the judge. This explains the confusion many felt following the ruling. Although the judge found in Christie's favour on this point, he handed the judgment to Miss Thomson on the grounds that because of her status as a special client Christie's should have drawn certain additional issues to her attention - including, in particular, the fact that copies of 18th century works had been made during a revivalist movement in the 19th century.

• Christie's argue that, as the reformulated claim was not put to them in the trial, they did not have a proper opportunity to defend themselves against it.

• Christie's will deny that they were negligent in not issuing Miss Thomson with a warning that 19th century copies of such urns exist. They will argue that they were, rightly according to the judge's ruling, confident in their attribution at the time of the sale and therefore had no reason to issue such a warning.

• The auction house will also appeal over duty of care. Whilst, during the High Court hearing, they conceded they owed a particular duty of care to Miss Thomson in the particular circumstances of this case, they will argue that their duty was more limited than that set out by the judge in his ruling. Whilst Christie's acknowledge that they had to use reasonable care in any advice they gave Miss Thomson on the date and quality of the urns, they dispute that they had any duty to advise on the risks or recommend whether or not the urns were a good buy.

The appeal should be heard within a year.

Miss Thomson failed to gain permission to appeal against the judge's finding that the urns were probably 18th century.