I found the offical book and the CGP book both useful sources of information.
One may explain a topic poorly but the other does it quite well, i recommend using both.
I did this for AS and achieved an A (i was far behind in physics as i didnt do the full GCSE so the books helped)
I also found them very good for A2, but everyone is different. Just use the books and the mark schemes as your main sources of knowledge.