@ vjmehra
OSF at Enstone has been recommended on here by
Zonkor, so you already know that there is a club which can do the training. Their web address is
Oxfordshire Sportflying Club - Operators of Enstone Aerodrome
Personally, I am not aware of any other club which can do TMG conversions for JAR/EASA PPL holders. If you look at their website, OSF also offer
ab initio NPPL/SLMG training as well as conversions for NPPL/SSEA and glider licence holders.
I don't have information on other organisations which may offer NPPL/SLMG training, so I have nothing to contributre on that front. You could however contact a few gliding clubs and check their web sites.