Ebay has agreed to help prevent illegal sales of treasures on the auction site to preserve Britain's heritage.

It will now work with the Portable Antiquities Scheme (PAS) , which will monitor antiquities sold on Ebay to ensure sellers have the right to trade them.

If a listing is illegal, PAS will report it to the Art and Antiques Unit of the Metropolitan Police and Ebay .

People who discover gold  or silver objects, groups of coins from the same findspot, which are over 300 years old or prehistoric base-metal objects must report these finds.

The British Museum, which manages PAS on behalf of Museums, Libraries and Archives Council (MLA), told Computeractive that many are not and important finds ending up on Ebay and other online sites is a real concern.

Last year it discovered that around 450 finds that should have been reported to the relevant authority (the local coroner) under the Treasure Act appeared on sites such as Ebay.

This may not sound a lot, but when compared to the approximately 576 finds that were correctly reported in the same year, the scale of the problem becomes apparent.

Objects not reported also lose their archaeological value and sites of significant interest and insights into our past are lost or devalued.

Chris Batt, MLA chief executive said: "For those who are selling items illegally, this partnership means we have in place a process to stop listings and take action against the individuals concerned.

"Doing so is vital because such activity is not only illegal but could also damage the archaeological record as, without effective reporting, valuable insights into our past could be lost forever."

The British Museum said in most cases sellers are innocently trading items on the web, unaware that their finds need to be reported.

"People don't know about the Treasure Act and what it applies to. Many of the antiquities that end up at Ebay are single items such as coins or jewellery such as rings or brooches; we are not talking about huge hoards," explained a representative for the British Museum.

Another problem is people not knowing who to report finds to. The British Museum said local museums are a good start as the reports of finds will end up with the local coroner.

In England and Wales, finders of gold and silver objects, groups of coins from the same findspot, which are over 300 years old or prehistoric base-metal assemblages found after 1 January 2003, have a legal obligation to report such items under the Treasure Act 1996 .

In Scotland, the legal obligation to report all archaeological finds falls under Treasure Trove . For further information and advice contact the Treasure Trove Secretariat at the National Museums of Scotland .

In Northern Ireland, there is also a legal obligation to report these finds and people should contact the Environment and Heritage Service , Northern Ireland for more information.

Ebay is the first website to reach agreement with the BM and MLA. To help educate sellers, it has liaised with the British Museum and PAS to create a guide to buying and selling antiquities safely on its site with advice about reporting obligations.

People can also find more information about antiquities, the Treasure Act and how to get involved with preserving Britain's treasures at the PAS website. This voluntary scheme was set up to record archaeological objects found by members of the public in England and Wales.

Every year thousands of objects are discovered, many by metal-detector users, but also by people while out walking, gardening or going about their daily work. Such discoveries offer an important source for understanding our past.

At the scheme's heart is a network of Finds Liaison Officers. They play a central role in publishing the aims of the scheme, recording reported finds, giving advice on finds recording, conservation and the Treasure Act.

They also give talks and lectures and encourage liaison between members of the public, metal detector users, archaeologists and museums.