Interesting debate in places this - I think it says a lot about the society we are living in.
If I was put on the spot, I'm afraid I'd have to say that the maths/physics knowledge req'd to take the groundschool is at or around GCSE level. A-Level ('pure') Maths then begins to concentrate on calculus and not much else. Mechanics 1 is mildly relevant, and may help for M&B. Other A-Level Maths modules, stats/discrete maths have no bearing at all.
In terms of the Physics, some ideas presented about things such as resultant forces, magnetism etc. may be of use but are dealt with in more detail than is really necessary. Here's the key difference between what is required of a pilot and a physicist: The pilot needs to know 1) What will affect him directly and 2) Roughly when and why this will occur. The physicist needs to know 1) A concept 2) The maths behind the concept 3) What experimental conditions are being used 4) To what extent his maths will be skewed by exterior factors 5)... the list goes on. As an example, a pilot may need to be aware that as water condenses, latent heat of condensation is released, and this will raise the airmass temperature. Physics A-Level will more than likely tell you the mass of the water vapour, its specific heat constant, its specific latent heat and asks you to calculate the energy 'loss' as it cools between two temperatures. Clearly this won't be necessary knowledge for the pilot. And so, in terms of pure academic requirements, GCSEs are fine, A-Levels unnecessary.
Where is this going? Well, despite this, I can't advise skipping A-Levels. Unfortunately we have had it imprinted into our heads that MORE people need A-Levels, MORE people need degrees. Without checking the exact figure, the government want ~70% of people coming through the education system to go to university. It's ridiculous. That must imply that 70% of jobs out there require a degree! And if you go to an interview for ANYTHING, odds are the guy sitting next to you has one. While airlines aren't necessaily focussing on your educational background, if it all falls through and you decide to go and get a job elsewhere, you'll regret not having a decent qualification to back it all up.
Another angle might be to say that having completed years of study of some very dry subjects demonstrates a committment and determination (and an intelligence?) that might be valuable qualities in a potential employee.
In terms of WHAT qualifications to go for...I'd give this advice. If being a pilot wasn't an option, what else would you do, and what quals would you need for that? Do you enjoy the subject? If not, is there not a possibility that you'll also not enjoy the career of choice?
One final word is on A-Level Maths. Whilst this is not necessarily relevant to an awful lot of careers, it is unfortunate that a lot of the content does prove very useful in many (and some unexpected) university courses!
Just my two penneth
A38