You should be able to add an SSEA Class Rating to a NPPL (Microlight) until Apr 2015 under the provisions of the NPPL 'Licence Allowances' document (a new version will be released next week). See the NPPL website.
However, under the madness of €urocracy, you won't be able to fly an 'EASA aeroplane' (e.g. PA28 / C152) on an NPPL (SSEA) after that date - only a non-EASA 'Annex II' aeroplane (e.g. home built or a Tiger Moth / Chipmunk / Bulldog and others).
You should be able to convert a NPPL (SSEA) to a LAPL(A) under arrangements yet to be released; this will be valid for both EASA and non-EASA aeroplanes. But you will still need your NPPL (Microlights) in order to fly Microlights.
And yes, it is indeed utter madness - but that's EASA for you!