As far as I understand you need a Class 2 medical for a PPL while you can self certify on a NPPL.
You need a Class II for the issue of a PPL but you can use it with a Medical Dec under specified conditions which will confine you to the UK.
The use of NPPLs in other countries is largely confined to Microlights where different countries have different non EASA rules that are not discimilar to the UK requirements for Microlights.