Re: just starting ppl
Well worth getting down to your local airfield and getting (at least) a trial flight before you tootle off to the US, just in case you find flyings not for you (unlikely but has happened). Would also get your medical too, if there's any reason you cant qualify for a Class II medical (the minimum required for a JAR PPL) you could always go the NPPL route in the UK (lower medical requirements)
As cg says, if you train solely in the US, you will probably find that you need some "conversion" training to fly in the UK, in particular RT, UK airspace eg MATZ's etc), and airfield joining (never did an overhead join in the US). Use the PPRune search function, you'll find loads of threads about this.
Good luck whichever route you take. Also keep an eye on PPRune, spare seats are advertised from time to time, you might get a bit of experience sitting in the right hand seat for 1 bacon buttie/hour or so.