Andy I am in the SE London area and although its a jaunt I have just taken my Chim for a light conversion and respray to Webb's (Bristol). They have a v. good reputation. Otherwise, Tower View in North London have a good rep, I think.
Cutmonster...so you went for plunge...have you had it back yet? That's where I was thinking of taking mine...apparently they'll pick it up...all part of the service (for an insurance job).