Thanks to all for advice. What I am beginning to realise is that while the CAA and UK regulations appear to state that an old PPL(A) is valid for international use, so long as operators abroad think that a JAR license is needed, then effectively a JAR license is needed. Since if no-one will let you fly their aircraft without one, its irrelevant what the actual truth of the regulation is !!
I guess I need to find the right form to fill in to get one. As stated above I expect there will be a cost, but hopefully no exams or tests to take.
Anyone know? I'm all up to date with medical and current aircraft rating.