You have a simple choice - convert to a JAA licence before EASA implementation, in which case the transition is seamless, or don't, in which case your national licence becomes invalid and, as things stand, you will have to pass the relevant licensing exams and skill tests to obtain an EASA licence
First I've heard of this. Were the CAA thinking of writing and telling me about this any time soon?
They want UK PPL holders to demonstrate radnav skills or else we get an NPPL
I assume one can "demonstrate radnav skills" by getting an IMCr? (I'm having to guess and assume here because the CAA haven't told me anything.)