Hi Danny_R
Loretta has said almost everything I want to say. Maths is always a good thing to have at A-Level. I wish I'd stuck at it and got a good grade instead of one of those pass grades (eek). Having said that, I did well in my other A-Levels and got in to uni on a Computer Science degree. Despite not doing well at A-Level maths, I found that any maths done at uni was done at some point or other at A-Level, so I had a bit of a head start. Anyhow, I managed to get a 2.1 in the end - if I'd worked a bit harder then I could have got a 1st, but hey...
I am currently studying my ATPL groundschool with Brisol. I got my PPL this summer. I've heard people mention that having maths is a must for ATPL, well it isnt, to be honest the maths I've encountered so far is no more than GCSE, and if there is some content of an A-Level standard, then it is treated as difficult maths, and they really push the boat out to simplify it. It works too.
To summarise, get good A-Levels and do a degree you really like. From the subjects you've chosen, you sound bright, so A-Level maths is probably well within your reach and will give you the edge. IT is good to have on your CV, but us Computer Scientists look down on it as not being very difficult (Its snobby I know, but true). Do this and your ATPL groundschool will be a breeze.
Other people may not agree with this, but its the degree that makes you really stand out - for example, I went for a preliminary interview with the RAF. The officer interviewing was looking for qualities that would make a good pilot, and one of them was a good educational background - I told him I have a 2.1 in computer science, and this immediatly put me in the same league as all other candidates, no further questions asked. Read what you like in to it, but it made me feel a hell of a lot more confident.
Good Luck!
Bodie