After more foolish frighteners, the conclusion is as above- 'a flying holiday does not constitute a course of study'.
Recreational flying is like diving or golf, courses and lessons, and does not require a visa, unless you are at Part 141 FAA accredited commercial training places (which you wouldn't, or shouldn't, be for JAA PPL purposes).
Why this negative attitude in UK that everything to do with private flying is complicated, delayed, difficult, expensive etc? It is not only because of our amateurish clubs, bad weather, cost of fuel, landing fees, VAT etc. and is it any surprise that so many people go to learn and fly in the US where the aviation attitude is helpful and positive?