 The tunnel mouth is the south end of Copenhagen Tunnel, the second  tunnel on the main line out of Kings Cross station. There are real  houses in the area, but the rear exterior of Mrs. Wilberforces  house is a set built in front of a blank wall. Exterior scenes at  the front of the house were shot on Argyle Street, about 3/4 mile  south (see goofs entry); the interiors are a studio set.