One interesting item is that one chap I was speaking to yesterday (airline capt) - was forced from a UK ATPL onto a JAR ATPL by his company (wont pay for UK licence renewals anymore).
Having now lost his non-expiring IMC privileges he approached the CAA - who said he had to flight test before they would them him back again - but they would give him the non-expiring IMC privleges - under the auspices of grandfather rights - and that it was stated that anyone going to JAR wouldn't lose privleges...
He is now awaiting further comment from the CAA as really this should be done without flight test and without charge....but thats the CAA for you...