IPZ,
I used the trial exam papers from Wiggleys and found that they were the best way of helping me to revise for the NPPL(M) exams. They are more detailed than the papers overall, but working through them I found I got a really good grounding & that helped me with confidence in the exams. I can't recommend them enough
You've got the Air Law book which is very good (same author as the exam papers) and presents a very dry subject in the least worst way possible.
Personally I found Cosgrove didn't give enough detail, you almost have to memorise it word for word to get a good chance in the exams. What I did was buy the Thom books (published by Airlife) second hand, and use them for the more detailed background when doing the trial exam papers. Some folks will say that you need the most up to date books, which is true for the air law if you're doing SEP but the rest are all ok in the older editions - I'm not worried about how they look on the bookshelf, I think I paid about £4 each for the books I bought, but you may find folks who will lend them to you. Also the AFE published books are fine as well.
I also bought the RT book in the Airlife series when I did my RT exam, I found that one *really* good as it is much more readable than CAP413, and the worked examples of VFR trips at the back helped enormously
One thing I would say is that early in your training I wouldn't worry too much about the exams, take your instructors advice on timing. Another couple of good books to read are "Propellorhead" by Anthony Woodward, & "Think like a Bird" by Alex Kimball. At this point in your training they are enjoyable & I found they were quite motivating (although in a microlight the chances of doing Kimball's trick of setting the power miles out & then not touching it until touch down is not really going to happen in such a low inertia aircraft)
Either way, enjoy you training, even the exams can be fun. PM if you have any questions on above
Regards
batninth