The Elgin marbles, Stonehenge and the Crown jewels are labelled "priceless" for good reason. But that may soon change under plans to calculate the value of all the heritage assets in Britain. The Accounting Standards Board (ASB), which sets the rules for number-crunchers, has issued a draft paper suggesting museums and heritage groups should value their assets for the first time. If the plans go ahead it could amount to an unprecedented heritage "Domesday Book", giving the value of everything from ruined abbeys to dinosaur skeletons. The move could provide a multi-billion pound boost to the government's balance sheet. At present only cultural assets bought since 2001 must be valued - merely the tip of the iceberg for the vast collections in many museums. The ASB said the new proposals, called Fred 40, should result in much more useful and relevant information about antiquities. Curators will be expected to make valuations only where feasible. It may seem impossible to put a price on Stonehenge, for example, because of its rarity. In this context, ''replacement value'' is a ludicrous concept. However, accountants might simply capitalise the annual income from the standing stones. For smaller historical artefacts and pieces of art it may be possible to gauge market valuations. Chris Herring, finance director of the British Museum, questioned the practicality of valuing the institution's 7m items. The finance director of another London museum said the "impractical" idea would involve huge cost. "There is not a market for a lot of the stuff we have, so how do you ascertain a value, and if you bought something for £2 150 years ago what is it worth now?" he said. The ASB argues there are good examples of accountants valuing unlikely objects. The Palace of Westminster was revalued last year at £1.13bn, according to the House of Lords' resource accounts. And surveyors have also managed to put a price on more whimsical edifices, judging by National Trust accounts. However, the National Trust does not value the contents of its homes. Nor do most museums, which are directly owned by central government and therefore do not take out external insurance.