Not at Oxford, idk about Cambridge. But there are loads of unis that just check to make sure you meet their minimum GCSE requirements and then rank people based off UKCAT (Southampton, Manchester, Newcastle, Sheffield, there are a few others too I think) or BMAT (Imperial). Exeter rank on predictions and UKCAT (you basically need 3 A* predictions for them). So check to make sure you meet their minimum requirements and try your hardest in the entrance exams, which are obviously by no means easy.