(1938, Edmund Gwenn, Ralph Richardson)

“I recall one of the scenes shows a family living in an old bus on some waste ground. Another scene shows a West Yorkshire Road Car Tilling Stevens single decker.” (thanks Andrew Porter)
The bus drives past in a night scene. It's West Yorkshire 215 (WW4258), a 1928 Tilling Stevens B10A:

The housebus scene is unfortunately not clear, but we appear to see two different rear staircases and one open top: