Most online purchases are covered by Distance Selling Regulations issued by OFT. Some of the threads in the Ebay section detail them.

At the end of the day it's a lot of fluff if the trader refuses to budge, but things do look good for you now. I have had a courier issue once and from the trader's side it was not a lot of fun.

Hate to say it, but the lesson is ALWAYS use a credit card.

We had a similar thing happen last year. In my case the trader would answer no emails, no calls, nothing. Then, being a sneaker 'b', I emailed them on another email address asking about a large order and got a reply, but they would not reply after that.

Finally I contacted the credit card company who immediately refunded the money. The ball was now in the trader's court as they had to come back to reclaim the money. They never did.

Through using eBay a lot I have also come across this:

https://www.moneyclaim.gov.uk/csmco2/index.jsp

Government backed, but never used it. Might be a useful bookmark for the future?