The following from the dreadful CAP 804, since 2016 annotated for "reference only". What we do not know yet is whether the UK CAA will re-instate the UK PPL with full international status after brexit. As the licence meets ICAO it should do. EASA only covers a small part of the world.
CAP 804 (reference only) Section 2
2.1.2 NPPL(A) (Microlight) or UK PPL (Microlight) to NPPL(A) (SSEA)
2.1.2.1 The holder of any UK issued aeroplane licence with a valid Microlight Class Rating or UK PPL(M) licence without restrictions who wishes to obtain an SSEA Class Rating shall:
a) produce the licence;
b) produce logbook evidence of currency on Microlight aircraft;
c) carry out such SSEA conversion training as is judged necessary by the FI(A) or CRI(SPA) conducting the training to achieve the required standard for the applicant to take the NPPL(A) NST and GST in an SSEA. This training must include:
i) not less than 1 hour of dual instrument appreciation;
ii) 2 hours stall awareness/spin avoidance training;
iii) differences training for Microlight pilots whose Microlight flying has been solely on flexwing aircraft;
iv) Not less than the 32 hours required minimum total flight time for the NPPL with SSEA Class Rating, which may be a combination of both Microlight and SSEA flying.
d) pass the Part-FCL PPL(A) theoretical examination in Aircraft (General) and Principles of Flight;
e) hold a valid NPPL Medical Declaration or Part-MED Class 1, 2 or LAPL medical certificate;
f) pass the NPPL(A) NST and GST in an SSEA. For the holder of a PPL(M) with operating restrictions, the requirements shall further include:
g) the whole of the navigation training required for the NPPL(A) with SSEA Class Rating;
h) the completion of a minimum of 10 hours total solo flying which may be a combination of Microlight and SSEA flying.