"You may have reached this page due to a known problem with some UK ISPs" with absolutely no description of what that known problem that they know about actually is. Very bad UI decision there.

I'm pretty sure I can guess what the problem is (the IWF filter, no doubt) but if I were an ISP and got a pile of reports from users simply parrotting that message I'd block the site completely until they improved it. It is like me as a programmer getting "I gots an error message" from a user who then says "oh, I didn't read it all" when I ask what the error message actually was.