Don't worry about the exam, my daughter could pass it based on what she's overheard me talk about, to say they set the bar low is an understatement
A really good book for CP in general is "Close Protection; The Softer Skills" by Geoff Padgham; it covers the importance of tact, diplomacy, communication, planning and mindset rather than firearms and ninja skills, all areas that are key in corporate work and skills you'll use on a daily basis on the job.
Best book for me was Close Protection - By Richard Aitch by rich Aitch I've read most of the above and the information was not made clear unlike Richards book. Down side is it costs a bomb but well worth it. 5/5 for me mate.
if you can find it cheap pick up the modern body guard.. now it says modern, the pics are from the early 90 but the main content is good and will help you through the course as each chapter covers a skill set so its easy to use the old colour sticky tabs and sort yourself out plus its recommened reading by ED EXCEL and all the books the guys above have suggested are good too especially the one by Rich H
I don't know what exactly you have to learn in the UK for your SIA licence but my favourite Book is "Bodyguard" from M. Lonsdale. Its from 199x but still the only book I found with no nonsense and an overview over all aspects of bodyguarding. Its mostly about the US but all the basic rules can be transferred to anywhere in the world. Take a look on ebay for one - even if it doesnt help when your doing the exam it will be of a basic guideline later on jobs.
For CP, Rich's book period the other CP books don't even come close, the reason we use this book on our course and it's given to the students to take away with them to compliment their notes and experience.
We also recommend Peter's book as the others don't come close and surveillance goes hand in hand with CP.
Indeed Rich's book is a very good read. However, you state that its to revise for the exam. Then I suggest you use your course notes as anyone's book, as good as it may be, may not cover what the exam is asking for. Considering most 'cp' courses are worth tuppence, a 'good' book may just mislead you.
Stick to your course notes, then when having passed the exceptionally easy test (it must be easy considering some of the folk I've seen with a badge) you can crack on and start learning for real!