From the PAS website
The British Museum and the Museums, Libraries and Archives Council (MLA) have partnered with eBay.co.uk to ensure that antiquities found in the UK are being sold legally on its site.
In order to prevent illegal sales of treasure, the Portable Antiquities Scheme (PAS, which is managed by the British Museum on behalf of the MLA) has set up a team to monitor antiquities sold on eBay.co.uk and to ensure that sellers have the right to trade them. Where the listing is illegal, PAS will report it to the Art and Antiques Unit of the Metropolitan Police and eBay.co.uk, which has committed to end illegal listings.The commitment is the latest development in eBay's on-going work with national law enforcement agencies.
Full announcement here