I found this book very useful when I was doing Business Studies at A-Level as it has a great amount of detail for both AS and A2 level.
The only problem is, is that the book is very large and very detailed, but all I did was look in the index for a particular topic, and I managed.
A very useful part of the book, are the vast amounts of detailed quick revision and essay style questions included, which help greatly when preparing for exams.
I found this the one of the most useful Business studies books during my course, because the revision guides only give quick, shortened guides which can often miss information out that can help your understanding of the subject.
For another useful, but less-detailed book try the green 'A2 Business Studies' by Andrew Gillespie.