Assuming you pass your physics degree then the ATPLs will be easier academic wise. Met and Gen Nav seem to cause the biggest amount of trouble but the comms exams are little short of a joke. Your degree will certainly be of benefit in certain areas. As Phil says lies somewhere between old O & A levels (not GCSE).
Over many years I have taught several hundred graduate level students on ATPL integrated courses. The biggest problems they tend to face is the volume of material (some highly questionable as to its relevance) in the amount of time (7-8 months) and of turning up on time in uniform everyday!.
So it's full on day time ground school and most students will be doing another 3 hours per night and work at weekends, though I would advise taking a least a day off. You'll have to accept the 'system' whatever your thoughts might be about it and just crack on with your goal and put your social life on hold. If you do this then all passed in 8 months then on to the fun bit. Ignore this advise then you'll be still doing ground school in 12 months with failed exams, re-sits & possible re-course or termination (though this is vary rare).
Uplinker has a valid point. Some students do very well (many now captains after 7-8 years) while others struggle or find nothing doing, if you can get accepted on a scheme this would really improve your chances - note NO GUARANTEES in this business despite what the sales people will spin you.
Last edited by RichardH; 10th Mar 2015 at 16:54.