Agree you can take basically any a-levels. I did NO traditional subjects and got offers from Russell group unis. Do what you think you will enjoy/do well in, nothing worse than a class you hate!
If your college/school does law a level I recommend it, if you like law you'll find it interesting and it gives you some good core knowledge. It will also help you decide you definitely want to do law and you'll get to go on some good trips/meet interesting people.
As for uni, you'll need to do a law LLB to qualify