Next, SLMG. This can be added to an NPPL through differences training, but since 17th September 2012, you must take a skills test as well.
If someone says otherwise and "signs you up", beware the wrath of the CAA if you have an accident or incident.
The rules changed 17th Sept with the adoption of EASA last year, although in fact the Air Navigation Order always said you need a skills test to add a rating to your license.
The fact that the ANO did not reflect agreed NPPL policy was pointed out to the CAA on several occasions...
The actual requirement is as stated in CAP 804 Part II Section 5 Part A Appendix 1 Page 8:
SECTION 3. CROSS-CREDITING LICENCES AND RATINGS TO NPPL(A) (SLMG)
3.1 Pilots with valid licences and ratings
3.1.1 NPPL(SSEA), or any UK issued Licence with SEA or SEP Class Rating to NPPL(A)(SLMG)
The holder of a valid NPPL(A) with SSEA Class Rating, or any UK issued licence with SEP or SSEA Class Rating who wishes to obtain an SLMG Class Rating shall:
a) produce the Pilot Licence (Aeroplanes) with the rating;
b) produce log book evidence of having satisfactorily completed conversion training with an SLMG Instructor on self-launching motor gliders;
c) hold a valid NPPL Medical Declaration or Part-MED Class 1, 2 or LAPL medical certificate.