MJ,
Not quite right there. There is a little loop hole in the CAA that allows foreign ATPL holders with +3000 hours total time and 1500 hours in command of aircraft 30 tonne or greater (etc) to aquire a UK CAA ATPL. You only need to do Air Law and Human Performance (plus the sim check with a UK CAA examiner). You are entitled to fly G reg aircraft only and you cannot get a JAA ATPL untill you have completed the rest of the exams.