Buses on Screen: The Day the Earth Stood Still (1951, Michael Rennie)

"There is a brief shot of what purports to be a London bus. In the same film there is also a brief shot of Westminster Bridge in London on which several trams are visible. There is also a brief shot of a PCC tram in Washington DC at the beginning of the film, just before the spaceship lands." (thanks Alan Sinclair)
The 'London' doubledecker is in fact seen in two different sequences; it's fleet number 2003 with the Fifth Avenue Coach Company. In the first it's clearly in an American setting (by 1951 it had found its way to California). In the second it is posed with a man in British police uniform, who obscures the fact that the driver is sitting on the wrong side! Curiously, the very modern fully-fronted body style and the destination 21 Piccadilly Circus make it look more 1970s Manchester than 1950s London.....this is the unique prototype 1933-built Yellow Coach Model 706 'Queen Mary'. It looks so modern perhaps because it's a 72-seat rear-engined doubledecker! It was actually Chicago Motor Coach Company 103. In this guise it also appeared in On The Town and The Snake Pit; it was wrecked by fire a few years ago at a museum in California. (identification by Malcolm Thwaite)

Colin Read notes Washington PCC cars 1256 and 1467; fleet name is 'Capital Transit':

Also seen are several buses, one with 'Colonial Historic Tours', the others with Capital Transit:

This street shot has several unidentified buses:

A view of London has a number of tramcars:

Buses on Screen > Films > Films D > The Day the Earth Stood Still (1951, Michael Rennie)