[Athelstan]

Rockhopper
I do not know what the legal situation is in UK, but here the provider of your own ISP has a duty to inform you (if requested) who the sender's ISP is and a contact address. You then take it up with them and they have a duty to either: a) block the sender or b) provide your legal team with the identity of the sender as evidence in proceedings. So why not try this out with your ISP? Good Luck.