Almost! The NPPL will cost £139
and you apply for it through NPLG Ltd which is based at Turweston; see their web site for more info at:
NPPL Home Page
As I understand it, one possible route would be for you to use your current PPL to receive differences training and then apply for an NPPL with SSEA and SLMG ratings on it at the same time, so that you don't have to pay for ratings fees twice.
The advantage of this route is that a) the differences training can be undertaken on any motorglider, whereas adding a TMG rating to a PPL must be done on a dual ignition aircraft such as the Dimona HK36 which they have at Enstone and b) it is only a paper shuffling exercise as opposed to the rating exam you would have to do with a PPL TMG rating.
The other advantages are that a) the NPPL is for life and b) the medical is only a declaration countersigned by your GP (cost me £25) and is renewed every 5 Years. Quite what EASA will to to the NPPL by the time they have finished is another matter, but that is the situation at present.
NPPL of course is restricted to <=4 seats, <2 tonnes, no IMC/IR or night ratings, but the French will now allow you to use an NPPL with an ICAO medical (see NPLG site for details) to fly in their country . . . . good for them
All of the above derived either from the NPLG website or from conversations with the NPPL folk at Turweston. If anybody has any further authoritative information, I would be interested to hear it too, as this is a path I am also considering.