Please don't let this thread become a general discussion about academia and qualifications in general; I will have to strip out anything I feel is irrelevant to the purpose of this forum - that is, getting an ATPL! I really don't give a damn what the equivalence of GCSEs to O-Levels is (or was), and neither the answer nor the discussion will help anyone. Do it in JetBlast if you want to have a rant about educational standards.
The ATPL exams are not difficult in the nature or level of the knowledge required. They are difficult simply because of the volume of study and the limited time in which they must be completed. They do not in any way approach the academic level of a conventional degree. For reasons mired in history, they don't even accurately reflect current science in aerodynamics and other topics, so the (rather shallow) knowledge gained is of little use once the exams are over. They are simply a filter, a hoop to jump through.
Because of the amount of study involved, some insititutions (such as the Open University) may give you credits towards degree studies for your ATPL and other aviation qualifications. That is worth following up if academic qualifications are of interest to you; to all other intents and purposes the ATPL has no academic value whatsoever.
Scroggs