York.
Well as there was 33 of them, not all would have been used on the London workings anyway, also photographic evidence suggests that they worked into London until late into their lives.
Lets face it though, locomotive design moves on, in their day the Midland 4-4-0 Compound was an express passenger loco but by 1930 they were being over shadowed by new designs that had greater 'haulage capabilities' - people still want to model them, because they were part of the 'scene' they are trying to capture...