Here is something i read on another post:
I would recommend the CGP revision guide. Can be purchased for £10.99 pretty much anywhere (WHSmith, Waterstones or other good book shops/online).
It is very good in the way it's simple, has a good layout and is easy to read, making it very worthwhile. It splits topics into chunks and they are explained as simply as possible. I am doing the same course as you, but they do specify what you need to learn for Edexcel/OCR/AQA A or B etc... Although sometimes they are wrong so be careful.
Their books are very informative but informal too, which makes them great to read.
I would add that they don't go into too much detail, but certainly help you to understand the basics and general concepts. If you solely revised the revision guide and learnt it all, I would imagine you could get a high B/ good A in unit 4.
Is this true?