We are looking to put our kids into a British school over here and the differences with the American system are primarily in how the kids are tested. In the early years there aren't many differences. Once the kids move on to high school they take tests to put them on to certain academic paths that are more rigid and defined than in the US system. These tests (called 'A' levels and 'O' levels) are of critical importance because they determine if your kids get into college or not, and also which college they can attend. I suppose it is similar to the SAT/ACT we use in the US, however you can still attend okay colleges with mediocre SAT scores as long as the other things such as class ranking and extracurricular activities are positive. Not so with the British tests- once you score poorly on the tests you are pretty much locked out of the UK higher educational system. Therefore, teaching in the British schools is very much geared toward teaching you to test well on the exams. The tests are apparently much harder than the SAT so this could be quite stressful for the kids. Some other small differences are things like learning rugby and cricket in gym class!
Most of the British schools here seem pretty decent to me and offer a much cheaper alternative to the US schools- definitely worth investigating if you are interested in moving to Dubai. I know a few people who homeschool over here and yes- it is legal.