Re: JAR Compliant PPL vs JAA PPL - Difference?
Caveat emptor!
Yes, an FAA PPL can be 'converted' into a UK-issued JAR-FCL PPL(A). But to do so, you will need:
1. To pass all the JAR-FCL PPL(A) theoretical examinations plus the FRTOL practical test. (If you have more than 100 hours on aeroplanes, then it'll just be Air Law, Human Performance, Communications (PPL) plus the FRTOL practical test.).
2. To hold a JAA Class 2 (or Class 1) medical certificate.
3. Meet all the JAR-FCL 1.125(b) experience requirements (not required if you have more than 100 hours on aeroplanes).
4. Pass the full JAR-FCL PPL(A) Skill Test with a JAR-FCL Examiner.
Bearing in mind that you can fly in the UK under Day VFR conditions using an FAA PPL, my recommendation would be (if you really must go to the USA) to train for the plain vanilla FAA PPL, then build up to 100 hours in the US or UK before converting to a JAR-FCL PPL(A).
And ask yourself why any school would 'voluntarily' stop JAR-FCL PPL training in the US...............