What GCSE results do you need to go into law?
Universitys don't say any specific GCSE's or A-Levels however you will need passes and good grades in "useful" subjects.
I think you should aim for as many A's as possible. Law is quite a heavy degree and fiercely competitive so high grades won't really set you apart. Of course they help but get some work experience under your belt, this will interest the best universities.