Windrushers Bicester Airfield: they did not return my email. Their website advertise that they can train for SLMG/TMG rating.
Wycombe Booker gliding club: they don't do it
Oxfordshire Sportflying Enstone Aerodrome: they don't return emails either, but they are still in business.
Lasham: their motor glider will fly again next year.
To fly a TMG under EASA rules, you need
- either a TMG rating on an EASA PPL(A) or any other aeroplane licence or
- a LAPL(S) or SPL (SPL stands for Sail Plane I suppose) with TMG privileges.
A NPPL(SLMG) should be, according to CAP 804, easy to convert into a LAPL(S) or SPL with TMG privileges.
I don't know of any way to get a TMG rating on a PPL(A) on the basis of a NPPL(SLMG)