Hello all,
I studying A-level physics as a distance learner with ICS. My advice is;
1) avoid ICS, the course is pretty substandard in every way. If you can find another place that does it and their materials look professional, then go with them if you're really unsure about going it alone with the syllabus and text books (which I think in fact is an entirely do-able option).
2) beware, you'll pay A LOT to do units 3 & 6; I only found two places in the whole of South England that do it, one costs £500 for the exam, £500 for the optional prep session I think (a place in London I can't remember the name of), the other charges £350 each for exam and preparation session, 3A Tutors in Bristol, the one I went with. On the other hand, if you're persistent, you should be able to find a good deal on the the other theory papers - I found a school that's only charged me £12-15 per paper!!
Good luck all!