the night rating here is an extra £800.
The night rating does not have to be an extra. It can be integrated into the 45 hours you need to fly for the JAA PPL regardless of where you do the PPL. In fact, the five night hours are a mandatory element of the FAA PPL, and that's 45 hours too.
In Florida, or basically with any intensive course, you can expect to be ready for your PPL skills test with a little less than 45 hours so you can use some of the "extra" hours till the 45 to do the night hours.
OTOH, if you do a part-time course over a year you will find that there will be large periods (three weeks plus) where you don't fly because of weather, vacation or other external factors. This will cause you to lose proficiency and may lead to needing 60 hours or more to be ready for the basic PPL, without having flown at night. In that case the night rating is indeed an extra five hours, most of them dual. Plus in Europe you've got to worry about landing fees, which are sometimes higher at night. Hence the £800 price tag.
So it all depends on your aptitude and commitment whether you can do the night rating as part of the 45, or whether you need to do extra hours for it.
hey if get my qualifications in america will i be able to work in britain?
aslong as you do a JAR/JAA PPL it should be fine. even if you do an FAA one i think you can get it converted?
To work commercially you need a CPL or ATPL. For carriers in Europe, most likely a JAA CPL/ATPL. The entry for a JAA CPL/ATPL is an ICAO PPL. It does not have to be a JAA PPL, it can be an FAA PPL as well. Or even one from Botswana. So if you intend to go commercial anyway, and if you want to do your PPL + hour building in the US, you might as well go for an FAA PPL. It's probably a bit cheaper and it allows you to start hour building straight after passing the skills test (since the examiner will write you a temporary FAA PPL license on the spot, with the final one coming via mail a few weeks later). Plus, it gives you a much greater choice of schools - there's only four or five JAA schools in the US, and maybe hundreds of FAA schools.
Bear in mind though that you will probably need an M-1 VISA. For this you need some paperwork, which can only be issued by a SEVIS approved school. All part 141 schools are SEVIS approved, but not all part 61 schools are. This will limit your choice of schools quite a bit. Not as much as the choice for a JAA school will limit you, but still something to consider.