Cambridge students gave a talk at my school, and one said they had multiple Cs at GCSE. I would believe them when they say they don't look at them. Also, the rule of thumb I've heard is that if you get 5 A*s at GCSE, you're the right callibre of student, in which case you're certainly fine to persure a degree there.
Edit: Just realised the original post is 2 years old. Nevermind lol