Welcome to PPrune.
Most people here would recommend you have a backup career in case things go wrong. As you will be aware airlines go bankrupt frequently, people fail medicals and pick up injuries over the years.
You should get a career which you are interested in and are good at. I decided to do a Law degree some people here have degrees in Geography, Accountants, Mech Engineering, Aero Engineering and many more.
Yes, Maths and Physics is a good for becoming a pilot.
Your A-Levels don't really mean anything in the real world I'm afraid, so getting a real career to fall back on will help you.