I think insisting on a .uk email id could be a problem. You would effectively bar all BT users (btinternet.com, btopenworld.com), aol users (aol.com) ...
There have been a few spammers joining up recently with .co.uk email addresses, so even that can not be relied upon.
O.H. dear, That's worrying, I guessed they would be outside the U.K. because of the Polish / French content. I guess if they can be traced to a U.K. ISP they could be reported a little easyer
Sorry, got to ask, what does "O.H." stand for please?