In reference to some of the other answers, let me just clarify first of all that you mean the Open University (www.open.ac.uk), not just any random 'open university'; in other words, the well established and globally highly regarded pioneer of distance learning?
In which case, as some who happens to have an LLB (Hons) from Open University, I can tell you that it was absolutely top-notch, especially their learning materials are second-to-none. I did mine alongside a busy professional work life plus family commitments, so distance learning was the only option for me, but in hindsight I would be happy to recommend the Open University law programme for anyone irrespective of their circumstances.
...having said which, it's not quite the same as doing a law degree at Oxbridge, is it now? Anyone who tries to tell you otherwise is fibbing. If you want to land a plum solicitor's training contract or a barrister's pupillage at a leading law firm, your chances go up about ten-fold if you have an Oxbridge (or at least Russell Group) vs. Open Uni degree under your belt (and no, it shouldn't be like that perhaps, but that's the reality even in this day and age), not to mention if you want to end up as a QC or some such big wig at the top of the legal profession. So in that sense nobody can really claim that the Open Uni degree is the 'same' as those others.
Mind you, it doesn't cost anywhere near the same, either, so in that sense the value-for-money that you get may be as good or even better than from some other law schools.
I think you need to be clear why you're doing a law degree first of all; I for one never wanted to practice law, I just did it for my own enlightenment, and the Open Uni served that purpose brilliantly. You also need to be clear on why you would want to study by the distance mode as opposed to the conventional full-time one; there are major pros and cons to both, and you want to make your choice for the right reasons.