I did Geology a long long time ago, IIRC, the south of the UK is sinking and the North is rising - not by much mind- so all of London is eventually doomed. I think subsidence is the wrong term though- its not like you are on top of a coalfield but yes, London clay does suffer worst with heave n shit dependant on local water- though much of the housing stock is 100+ years old, so you would expect some evidence of movement- it doesnt help that fpoundations are pretty shtty for mist local victorian stock either