After thinking about it, I did a little checking. The policies of eBay UK are identical to those of the US eBay. You might want to read this and this. EBay UK does not send emails threatening legal action of any kind:
Quote Originally Posted by eBay
Once the seller files an Unpaid Item dispute, eBay sends the buyer an email notification and displays a pop-up message if the buyer signs in within 14 days of the filing.
They will also send multiple emails politely requesting payment, and will not begin the Unpaid Item procedure until the seller has attempted to resolve the dispute with the buyer directly. Chances are it was the seller himself sending the threats, in which case he is in violation of eBay's published policies. Check the email header to see if the FROM field was spoofed, and to ensure that it was sent from eBay's mail servers.
Beeblebrox.420 Reviewed by Beeblebrox.420 on . ebay threaten legal action over £20 I owed ebay £20 and today they sent me a letter threating to send BALLFIS round and to take legal action over me for NOT PAYING £20 :| THERE FUCKING MILLIONAIRES Rating: 5