Interesting -
As far as I know, the only way to "use" your account is to either crack the password (guesswork or brute force), or else obtain the password by a keyboard logger or other spy software installed on your PC.
I would tighten up your firewall, AV and anti-spyware defences, just to be on the safe side.
How can the items be for sale in the US if your account is registered in the UK? And what benefit would it be to the "seller" if payment were sent to you?
I wonder if it is possible for ebay's systems to allow a near-simultaneous registration of accounts with the same name in different countries, which then get "merged" when their systems replicate information.
SD