I recommend that you don't ever stick with just any one source of study material be it Oxford, LBP, ATC Perth or whatever.
There are a bunch of well known reference books that you'll need to get a hold of, they'll be listed in the License notes you get from any of the well known providers and of course a set of CAAIPS will never go amiss (Down loadable for free off the CAA site).
If you find yourself struggling with any given module, the mob should fork out for an "in-house" course as past of your re-settlement when you get into your last 18 months - well they use to!
I did mine after I got out and I think it would be easier to get your head around the legislation side of things if you were working within the system, the amount of tea breaks and lunch breaks I gave up to visit the tech library of my various locations still makes me shudder! Plus there is always experienced license holders to pester for info.
Good luck though it's worth the slog if you want to remain in the game.