Scoobster
Try asking schools if they offer the "IMC Rating" as most do, but are unaware of the new name. In my experience, when contacting places regarding the IR(
R) most are quick to respond with "No, we don't do instrument ratings"
These may be a bit far from London, but there's a good little school (which few people know about!) in Bournemouth who teach the IR(R). It is true that very few places teach the CB-IR, though Airways at Exeter do and have a very good reputation.