From a BR publicity booklet entitled British Rail Is Travelling....1970, comes this shot of an unidentified member of the class on the outskirts of the capital. Initially, the exact location of this scene was somewhat of a mystery until the following was provided:- The location is between Royal Oak and Westbourne Park, three-quarter miles west of Paddington. This ladder crossing was called Subway Junction. The train was routing Down Main to DR No.2, so probably going out to Old Oak via Kensal Green servicing platform. It was blocking all routes here, something of a 'last resort' operationally. That makes the most likely time about 9.45am. As for the date, it has to be 1970, immediately after the remodelling/resignalling of this area, which I think was completed that year(?). The photo was taken by an employee (empty train) so I'd guess it was taken to accompany something written about the remodelling (i.e. magazine or BR document).
(Thanks go to Peter Wild for his knowledgable information!)