To get into the very top Maths Universities you will need at least A*AA at A level in some cases A*A*A. These grades apply for Oxbridge, Imperial, UCL, Durham, Warwick, Bath, Bristol and Exeter plus others. Your C in Geography wont matter. Outside of these most will accept you. There is also a problem in that most of the above prefer students with Further Maths at A level. Step is required for most of the above but nowhere else. With AAA you would likely to get into the likes of Birmingham, Manchester, Leeds, Kings, Loughborogh, Lancaster and East Anglia amongst others