I have the same licence JAA CPL (A) R and am in the process of upgrading to JAA ATPL by putting my overseas 744 rating on it with the old National exams. You are still rock solid as long as you don't let your IR lapse more than 7 years as they will drop down to CPL credits and you will loose your ATPLs.
I received this info from the CAA and it is also in LASORS section A. It is difficult to find it in the preamble but keep at it and you will get there.
Let me know how you get on.
The Cav
