Abz, I really would suggest you should concentrate on your A-levels. If the TATC studying is in any way comparable to the ATPL studying, then it will be very useful to you to be able to have done them. It can also show that you are keen to study to the recruitment people which can't be a bad thing.
Then again, I didn't get as good grades in A-levels as I'd hoped, so made myself even more determined to get a good degree.