(1942, Greer Garson, Walter Pidgeon)

Colin Read notes: “In the opening scenes of 'Mrs Miniver' there is a view of Hollywood's idea of a London bus, a normal control creation (!) showing 'route 39' bound for Southfields Station. Interior view also.”

The body appears to have been built on a conventional American truck chassis; it seems to be the same vehicle seen years later in two 1958 movies, Merry Andrew and Darby's Rangers, also Royal Wedding. Note that here it's in a reasonably convincing wartime London Transport livery, rather than mostly red. The interior footage includes a back projection of two genuine London Transport 'deckers, one appears to be an AEC NS:

The rear of the bus appears to carry two separate registration/licence plates: