Hi, my son is in similar position although luckily he gained a high B at GCSE maths. He has done a lot of research into unis that don't require the A level, and although, yes, the most prestigious unis do require A2 or AS maths, the rest do not. Newcastle doesn't oddly. And many of the others only require C at GCSE.
Having spoken to tutors at open days they say the maths required is taught on the course. If you enjoy programming (which you do!) then the type of maths required for CS is prob the type of maths you are good at so don't be deterred - please!
My son is going to put a couple of foundation years on his UCAS form - Liverpool do their foundation year at Carmel College which is a great college and even Loughborough have a foundation year CCC requirements but only if you haven't studied the required subjects (in yor case maths) and not for those who didn't achieve the grades.
Hull and I think Sheff Hallam only require C GCSE maths.
Best of luck! You aren't after all applying to Cambridge so these things are still within your grasp.