Yep, converting the licence to an EASA one is a ball ache of the highest order.
The UK CAA used to issue a JAA ATPL valid for G-reg aircraft if you had 1500 hours in command of 30 tonne a/c or greater (etc) but that loop hole has been closed now. Note, if you wanted to fly for a different country, e.g. Ireland or Portugal, you'd have to do the rest of those wonderful exams...