The plea coincides with news of an explosion of interest in archaeology, with more than 47,000 ancient artefacts being dug up by members of the public last year.

Hundreds of objects are being unearthed and sold illegally, to the alarm of experts.

The Treasure Act of 1996 stipulates that finders have a legal obligation to report potential treasure finds such as gold and silver objects more than 300 years old.

Roger Bland, the British Museum’s head of treasure, called for eBay to remove potential treasure items from its website.

Casting his eye over eBay’s current offerings, he expressed alarm over a Roman silver ring, which is said to have been found in Luton.

It is “a potential treasure item” because it is Roman, silver and found in Britain.

The problem, he said, is that eBay has told the British Museum that it will not remove an object from its website unless it can be proved to fall within the criteria of the Treasure Act — primarily that the objects are gold or silver and older than 300 years — that it was dug up after the Treasure Act came into effect in September 1997, and that it comes from this country. Many more artefacts that appear on eBay are not from this country.

Dr Bland said: “My hunch is it’s a recent find rather than an old one. We can’t prove it. But eBay won’t take them down unless we can prove these things. They should take them down. No reputable dealer would sell objects if they weren’t sure of the provenance. We’re seeing a significant number of potential treasure finds being sold there.”

In a random search of eBay’s site yesterday, The Times found 420 “British antiquities” for sale. They covered a job lot of “metal-detecting finds”, including a seal matrix of the 13th or 14th century. The description noted that the objects were “all as found with only loose soil removed”. Like other entries, provenance details were conspicuous by their absence.

Dr Bland also heads the Portable Antiquities Scheme, a voluntary code to encourage the estimated 10,000 metaldetector owners in England and Wales to report all finds to local museums.

He fears that up to five potential treasure items are found every week and quietly sold off without experts being given a chance to study them. Important information about our heritage could be lost, experts caution.

A spokesman for eBay said: “eBay is in discussion with the Portable Antiquities Scheme (PAS) and the Treasure section of the British Museum to establish a formal agreement and a notice and take-down procedure, whereby eBay will remove illegal antiquities from eBay.co.uk upon notification by the Metropolitan Police Arts and Antiques Unit, who will be acting on reports sent in by the PAS/British Museum.

“In the meantime, whenever we are informed by any authoritative third party that they believe an item to be illegal, we take that item down.”

Some finders also wrongly assume that they can make more money by selling an object through the internet. Dr Bland said: “We find they get less on eBay. eBay prices are a lot lower for a lot of things.”

Bidding for most of the antiquities on eBay’s site were below £100. The Roman ring’s starting bid was £7.99. An object which might come before the Treasure Valuation Committee and be said to be worth up to £1,000 to the finder if a museum purchases it may sell for just £100 on the internet.

Hedley Swain, the Museum of London’s head of early London history and collections, said: “We have got to change the law so that objects found in the ground are not automatically owned by the landowner. In Scotland, everything found is owned by the Crown. But land property is so important in England.”

Dr Bland stressed that the “great majority” of metal-detectorists are honest: “A small minority of hardcore people are doing this. What maddens detectorists is the idea they’re all like this. It only takes one or two bad apples to spoil the whole thing.”

JEWELS IN CYBERSPACE

• Roman silver ring, found in Luton. Starting bid £7.99, with 2 hours, 44 mins left
• “Metal Detecting Finds”, a collection including a seal matrix of the 13th or 14th century, a medieval beehive thimble and a Tudor buckle found in Kent. Description: “All as found with only loose soil removed.” Bidding, which had reached £13.41 mid-afternoon, ends today
• Rare Viking bronze horse harness pendant, with an interlaced animal design, found in Melton Mowbray. Circa 8th-9th century AD. Bidding reached £17.99, with 5 hours, 54 mins left
• Religious Celtic bronze bird vessel decoration, circa 1st century BC, found at Melton Mowbray. Bidding reached £11.50 with 5 hours, 51 mins left
• Medieval 14th-century brooch in copper alloy, described only as “UK find”. Bidding reached £11.50 with 3 hours, 45 mins left
• 14th-century hollow shank bronze doorkey, found in Durham. Description: “This is a truly exceptional find from the 14th century.” Bidding reached £205.23 with 4 hours, 49 mins left

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