As already mentioned above Bristol Ground School (BGS) has a very good reputation. CATS is also well known, they provide a full time course as well, which in my opinion is the fastest way to get the theory out of the way. But be advised, don't underestimate the time and effort you have to put in to prepare for and pass the ATP exams, this is not an easy affair! Good luck!
Last edited by Transsonic2000; 22nd Sep 2015 at 02:19.