PPL theory
Hey Jamie,
I would recommend against studying ATPL manuals in order to pass your PPL theoretical exams. You might not believe this, but I think you would actually do worse on your PPL exams having studied from ATPL manuals compared to dedicated PPL manuals such as those produced by Trevor Thom/OAA etc Why? for the simple reason that most of the content found in ATPL manuals is irrelevant to what is required of a private pilot and that of basic VFR flight. You'll also find that the majority of PPL style questions in your ground exams will be harder to answer if you've studied from a manual where a mere 5% of the content relates to your PPL syllabus. You do the maths!
If you really want to give yourself a head start, I would say get stuck into your PPL manuals before you even look into getting your ATPL bricks. Once your armed with PPL theoretical knowledge, you'll find the learning curve required for ATPL theory will be reduced somewhat and allot of the concepts & terms being used won't sound too foreign.
.Aero