hi !
A friend of mine just converted his UK CPL/IR & Fzn ATPL to a JAR CPL/IR .
experience : 700 hrs no Multicrew time .
He retained his UK licence and the UK APTL knowledge and thus got both licences valid !
When He meets the requirements for A JAR ATPL , he will convert his UK fzn ATPL to a JAR ATPL ..
He did it a month ago ... so patlolo , check with the CAA , It might have changed again !
good luck
WYS !