Hiya,
I have been looking for a really good Mini servicing/modification place in London for a while and asked your advice a while ago, after trying Lohen and GTT I got a couple of mods done but was having problems with my back suspension clicking. Most of the really good places are a 250 mile round trip away though!!
I found this guy called Joel in Putney, South London who is ex-BMW and was brilliant. Really honest and helped fixed my problem and was really knowledgeable. So just thought that I know it can be really tough to find people in London, so if anyone was after a good mechanic let me know and I can put you in touch (I know I'm not meant to advertise on here but they haven't set up a website yet so thought this may help everyone out in the meantime)
Jay