Whist the ATPL subjects do not require any Maths and Physics Knowledge beyond GCSE, doing them at A Level will help a great deal in training your brain to think in an scientific/ numerical way and enable you to visualise concepts so much easier.
With decent GCSEs in Maths and Physics you will have enough basic knowledge to take on the ATPLs, if you do them at A Level and get decent grades you will eat the maths/ physics based areas of the course for breakfast.
Re French in the ATPLs, any one remember this question :
What is meant by the abbreviation HJ with respect to Aerodrome Opening times?
"Hors Jour", french for daytime hours! Knowing a bit of French helped me get that one right.
Might be worth doing a language or two at A Level if you think that in a future airline career you will be highly likely to be flying to foreign countries. What better way to woo the foreign hotties than impressing them with your knowledge of their own language. Personally id choose Portugese if your school offers it, those Brazillian girls do it for me every time!