If you go to Florida with the attitude of "I am here to get my PPL in 21 days and not for an easy ride holiday" then you will most likely get your PPL.
I done mine in 21 days exactly in Florida. I sacrificed nights out in Daytona for the study books. You really have to be 100% dedicated to the study, schedule and rules or you will not do it.
Get as many exams out the way as you can before you start an intensive course, it really will make the load a lot easier.
Personaly i think it is the best way, once you get home book in with the local flying club for at least a few hours to get used to RT and procedures in the UK. Then i would recommed befriending a good pilot with plenty of hours and experience and go flying as much as you can with them.