Peter Kerslake says "Having lived in Chippenham I am confident that this is a Bristol to Paddington working heading eastwards towards Swindon and beyond with part of the extensive Westinghouse Brake and Signal Company factory complex in the background, and that the uncleared signal is for the Calne branch line which headed away from the eastern side of the station.
The escaping steam from the safety valves spoil this image somewhat as Old Oak Common's 5040 "Stokesay Castle" sets off homeward bound, the engine being a long standing resident at Old Oak Common for much of its working life before going down to Bristol Bath Road depot in October of 1961 where it survived until being condemned in October 1963."