The Thames Valley and Thames Valley II are supposedly descended from the two strains originally used as a mixed culture at the old Brakspear brewery in Henley. I've used the 1275 and it is very crisp, clean, and neutral... it was probably the reliable attenuator in the blend, with the other one providing the character. (The Brakspear brand has been sold on a couple of times since they shut down, no idea what yeast is currently used. For a while one of the owners continued to use the dropping system, but I doubt there's any continuity now, if anyone is even still using the name.) By the description, I suspect the White Labs Thames Valley (WLP030?) may be more closely related to the one you're after. But it's a Vault strain too, so no real help there.