I now see that until Sept 2013 at least, you can fly PPL on a medical declaration (if I got that right).
That option is not available for a pilot with a lapsed licence / rating.
I will be calling the CAA for clarification,but is there anybody here that really understands this stuff and can advise me.
They will probably ask you whether you have read CAP 804! I suggest that you read the relevant sections before pestering the CAA.
If you wish to fly both EASA and non-EASA aeroplanes, the simplest option for you is to renew your SEP Class Rating by flying the SEP renewal proficency check and apply to the CAA after 17 Sep 2012 for your licence to be reissued as a lifetime part-FCL PPL(A). If you wish to downgrade that licence to a LAPL(A) with reduced medical requirements, you may do so at any time.
If you decide instead to choose the NPPL with SSEA Class Rating, you will need to meet the requirements stated in
http://www.nationalprivatepilotslice...20REV%2009.pdf page 7 para. 2.2. However, the NPPL will not be acceptable for use on EASA aeroplanes after 8 Apr 2015.