Dave,
I would do which ever subject you think you have the best chance of getting good grades.
If you are good at Maths and Physics, well study for them. But, if you're crap and hate them with a passion, but choose them because BA or other aviation companies 'prefer' them, when you get your results you might not get the results you want.
What Im saying is study the subjects you are interested in and enjoy. If you hate something you will not put the required effort in when your bored and pi$$ed off with it.
How many Captains out there have A Levels, HNDs and BA Hons Degrees in everything but aviation related subjects? When interviewed, it would look better if you made the wise choice of a degree in Basket Weaving and got the highest grade than choosing Rocket Science and failing.
See my point?