MFWF,
Have you considered joining the
Volunteer Gliding Squadrons ? who also instruct on the Grob 109 (a TMG/SLMG). Given you've already got a services background with flying experience I'd thave thought you'd stand a good chance. The only downside is that I think the nearest unit to you is
RAF Odiham, and I think it involves giving up a lot of your weekends.
As its run by the services, they train you (so you don't need a CPL or FI).
I'm sure that there are one or two on these forums who could tell you a lot more.
Brooklands