Some points may I hightlight for the 16 year old wannabes here.
Usually to be succesful at ATPL, you need to be reasonably at hand with mathematics, this does not mean to say you need A-Level maths to succeed.
There is no set entrance requirement for entry into any ATPL course by the CAA, however if there are any, it is by the institution itself. The highest qualification requirement I have seen is GCSE maths C, but even so, you can still get in without it!
I dont think there are any strict formal qualification requirements for entrance into any ATPL course.
However having said said that, you should be moderately good at maths and physics to be succesful.
A-Level Physics is an excellent qualification, if you want to be a proffessional pilot. Theories such as, Flemmigs Left Hand Rule, Electromagnetic Induction, Forces equations, Gas volume density and pressure and many other concepts would already be familiar to you before you even start your ATPL course, hence you will find it easier in your ATPL study.
However ATPL is made to be a stand-alone course - you dont have to have a physics A-Level to be succesful.
The level of mathematics at ATPL is fairly moderate, about GCSE level. But obviously, the better you are at maths, the more comfortable you are with any maths in the course.
I highly recommend A-Level mathematics if you are doing A-Level physics as they both go hand in hand and you will find that maths helps you with physics and vice versa.
Logical thinking and being good at mental maths is what really important in being a pilot, and that would be the most important thing you gain from an A-Level in maths and physics, if you do them.
The advanced maths content of A-Level maths would probably be irrelevent to ATPL, as only basics (such as trigonometry) is needed at ATPL. However I am sure it will help your ATPL, if you become super good at the types of maths in ATPL by taking A-Level maths.
Having said all that, I have not started my ATPL yet (starting very soon), and what I have said is based on the pre-course reading I have done so far to get a head start on ATPL. I have just finished my A-Levels one of them was physics which is why I can say what I have said.
Hope I helped.