If you are talking NHS, you probably don't have much of a choice. All the NHS GP surgeries have very restricted catchment areas. Have a look on the NHSdirect website. That'll tell you where you are likely to be able to sign up. Then you can come back on here and ask for the yay or nay of particular doctors on there.
yes....the blackfriars medical centre, colombo st se1 - i think you will be in their catchment area - they are great - ask for Dr Lefevre, a French female doctor - she is the best of them all. The Aussie nurse is good too - even the reception staff are friendly but firm - can't recommend them all highly enough !