FWIW, I seem to recall that very few (if any) UK schools would allow a new customer to self-fly hire one of their machines without some sort of check ride, even with a JAA PPL(H). The general consensus was that a new customer who hadn't flown in the country before (ie had done all of their training in the US, even if it was to JAA standards) would require more 'familiarisation training' than someone who had trained in the UK.
Agreed, some PPL holders will take 1-2 hours for this, others longer. I taught a chap who had a PPL from South Africa and it took him 17 hours to get used to navigating, talking in UK airspace etc.
Also don't forget Bristow Academy only offers PPL on a Hughes 300, and there are not many schools in the UK who operate that aircraft.