From the
www.nppl.uk.com NPPL website (FAQs):
Q: What do I need to do to fly microlights on my 'Group A' licence?
A: If you have flown microlights on your CAA issued 'Group A' licence since January 1999 and have remained current by obtaining a certificate of experience every 13 months then you can have a microlight rating added to your licence without any additional testing or training under "grandfather" rights . If you have never flown microlights on your 'Group A' licence but wish to start, then you will need to undertake type conversion training leading to a GFT, which you must pass together with the Microlight Ground Oral exam, before applying for the addition of a microlight rating to your 'Group A' licence.
If you have a JAR FCL PPL, then you will need to undertake type conversion training leading to a GFT, which you must pass together with the Microlight Ground Oral exam, before applying for the addition of a microlight rating to your JAR FCL PPL.
All applications for the addition of a microlight rating should be made to the BMAA on NPPL Form 102M, available for download on this website, accompanied by a cheque for £64 made payable to the CAA or alternatively the payment details must be completed on the NPPL Form 102 if payment by credit/debit card is preferred.