People who apply to Oxford and Cambridge are usually in the top 1-2% band of intelligence for their age range. Yes, of course you will need top A Level grades but these universities do look at your GCSE results too. They will not even consider you, regardless of what it says on their websites, unless you have top GCSE grades.If you don't have 10 A*s at GCSE then maybe save yourself the rejection by applying to other universities instead. If you still think you want to risk it, make sure you are outstanding in your personal statement, admissions tests and, if you get that far, blow them away at interview! Good luck.