The exterior of the BBC (Radio) building, and the foyer area, were the real BBC Broadcasting House building, shot in the 1990s, before the building of the New Broadcasting House extension 20 years later.
Meissen is a city located near Dresden, Germany. Both of these German cities are world famous for the manufacture of exquisite porcelain-ware.
This story can be found in a couple of collections of short stories written by Agatha Christie; "Poirot's Early Cases" and "The Underdog and Other Stories".