Your GCSE subject choices aren't that important. Your A-levels choices however, would be. A-level Physics and Maths would be essential, and Further Maths or Chemistry might be useful (or even preferred, for some universities). Thus, if you have the option, taking more maths/science options at GCSE may be worthwhile; however you aren't going to be accepted or rejected based on GCSE subject choices (it's unlikely you'd be accepted or rejected even on the basis of GCSE grades alone).