Unfortunately, having spoken to potential employers Id say you must reconsider London, a London law degree is considered second only to an oxbridge one, obviously you must discount somewhere like City Uni (if they do law) from that statement but London is the place to do law, that is if you want a successful city career.
My mothers Bf works for a large Oil multinational in London and their law department specifically mentioned the london law degree graduates, and their caliber due to the degree.
But. If you are set on choosing one of your aforementioned Uni's Manchester should definitely be your first choice (AAA) kent your safe second (320 tariff/ABB)
Which London universities do you mean? I know that UCL, KCL and LSE are very good universities but what about the rest? I thought that most of the other universities in London are not very prestigious. And I have another problem. Living in London seems to me very expensive. Is it really so?