If you were planning to apply to law firms after your degree, some of the big City firms in London (assuming this was your goal) do have A-level minimums in order to apply to them, usually hovering around AAB-ABB. It's important to note however, that if your goal was to work as a lawyer at a top firm, not ALL of them have an A-level minimum. In fact, it's a practice which is increasingly being removed from a firm's application procedure.
Most, if not all, firms will all require a 2:1 at university however. In reality, a 2:1 in Law from any university will open the doors in jobs that you'd likely want to be doing for the rest of your life. Just make sure you're somewhere that *you* want to be, and work hard at it! Your degree will only make up one part of an application, having a well rounded application is a lot more important.