Todd-AO only develop neg stocks in Super 8 e.g. 200T & 500T. They run their baths Tuesdays & Thursdays when I last checked.
The Widescreen Centre don't develop any Super 8 themselves, they farm the work out, almost all of it to Germany.
Film & Photo in Acton can in theory develop Super 8 E6 reversal, but the prices that they quote are so extravagantly exorbitant that you could probably fly to Berlin, get you film developed there, stay in a hotel, have a beer-drenched night out with a 3 course meal, AND still have spent less money than if had taken it to them. Although they do have the equipment & the ability to process it, I get the impression that they're not really interested in Super 8.
I'm not sure if this is the case, but I think that Nowhere lab might be able to develop Super 8 B&W as neg. Could well be wrong though...
There are other companies that handle Super 8 processing in London (but like Widescreen don't do it in-house), including Sendean and Blue Audio Visual. At which point I must declare my personal interest, as I am a director and co-owner of Blue!