BEagle replied
"Hi,
The issue here is "When is your PPL(A) SEP Class Rating due to expire?". If the date in your licence has passed (even by just one day), then as well as the medical, you will need to fly a SEP Class Rating renewal LST with an Examiner - even though your NPPL may be valid. I have a horrid feeling that you may also need to revalidate the JAR-FCL TMG rating...but I would need to research that.
But if it's only the medical which had lapsed, then once you've got it back, you can fly on your PPL(A) again with no further formality. But make sure you get your Class Ratings revalidated before the expiry dates in your licence 'Certificate of Rating Revalidation' page."
Class ratings expired a couple of years ago, so it seems I,m screwed.
Seems rather odd tho'...same aircraft, same airfield, same pilot, same air....yet I need a re-test.
Anyway, thanks for your help.