Hi there.
I recently went from Zero to fully qualified JAA PPL(A) in 45.2 hours (20 days) at a CAA/JAA certified flying school in San Diego, USA.
Very hard work to fit the hours into 3 weeks, so I would recommend getting all the written exams done in the UK to give yourself some relaxation time when you are there. Think very carefully about where you go and the time of year. Florida + Summer = potential for storms. California climate is much more benign. I lost about 1 mornings flying due to poor weather in September.
Absolute nonsence about US trained pilots on accelerated courses being less safe than UK trained pilots. Do you honestly think the CAA/JAA would issue licenses without a UK "checkride" for US trained PPL if that was the case?
Go to America, Enjoy the weather and the considerably more friendly skies, have probably the most rewarding 3 weeks of your life.