They differ quite a lot in training (especially with regard to theory) and your licence privileges will be different. You will have much less freedom with an FAA PPL(H) in the UK than with a JAA PPL(H).
There ain't no such thing as a PPL(H) IMC rating and you can't get an NQ until you have 100 hours post-PPL qualification i.e. until a minimum of 145 hours!!!
If you already hold a JAA PPL(A), you should have heard of LASORS; all the information is contained within! If you already hold an FAA PPL(A) and are in Lytham, then you should know the differences.
Cheers
Whirls