I did my PPL(H) in 12 days (Florida - FXE, which was great). However, I already had my written exams done since I then had CPL-MEI. I could have completed it in 10 days since I lost two days on arrival due to some screw up with scheduling. I admit it was hard work, flying twice a day and in between preparing for the oral exam.
My suggestion is to get all formalities done including medical and written whilst still in the UK. That way you save lots of money and time.
Written can be done at Farnborough - Flight Safety +44-1-252- 554-599.
Having completed this you prepare yourself by getting the practical test standard.
If you want to go to an extended holiday it also gives you more time to to "relax".
Ps. Make sure you don't need a training visa, as I know of one case where the US gov deported the poor fellow due to lack of said.
Pps. Most afternoons can be written off in Florida, due to thunderstorms.