There is no such thing as an SLMG in EASA-land, there are only TMGs & self-launch sailplanes.
In the recent JAR past the CAA would allow you to fly both on your PPL with an SEP rating (although not allowing the hours for SEP revalidation unless you had a TMG rating.) EASA does not allow the CAA any such discretion - you must have a TMG rating to fly a TMG (unless a student pilot under supervision.)
You can get a UK only NPPL(SLMG) with very little effort but, as previously mentioned, it will only be usable on non-EASA TMGs after April 2015. An NPPL(SLMG) is obviously convertable to an LAPL(A) with TMG but as you know you can't hold the two (A) licences. I think you should ask the CAA for a definitive answer: "What if I hold a PPL(A) (or CPL(A)) with SEP & at the same time an NPPL(SLMG), can I convert the NPPL(SLMG) to a TMG rating?"
Either they downgrade your PPL or CPL to an LAPL (can't see that happening) or they allow the NPPL(SLMG) to convert to a TMG rating on a PPL/CPL.
Last edited by Prop swinger; 20th December 2013 at 21:11.