You say you would like to fly microlights.
Your old licence included - even though you may not have known it! - "Microlight privileges included in such licences".
NPPL cross-credit rules - from NPPL web site - are:
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4.2 Pilots with expired licences or ratings
Credit shall be given for holders of expired CAA-issued JAR-FCL Pilot Licence (Aeroplanes) and UK PPL(A) licences or ratings as follows:
a. Where a Microlight class rating or Microlight privileges included in such licences has expired by not more than 5 years, the licence holder shall hold a valid NPPL medical declaration or JAA Class 1 or 2 medical certificate and pass the NPPL GST in a Microlight.
b. Where a Microlight class rating or Microlight privileges included in such licences has expired by more than 5 years, the licence holder shall undergo a course of training in a microlight aircraft as specified by a Microlight FI, hold a valid NPPL Medical Declaration or JAA Class 1 or 2 medical certificate and pass the NPPL GST in a Microlight. The licence holder shall also pass an oral theoretical knowledge examination conducted by the authorised examiner as part of the GST.
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So, in summary, GST if less than 5 years expired; whatever training is required to get to test standard, GST and ground oral if more than five years.
So no written exams, no cross-country nav test and no supervised solo.