The Driver is leaning out.

Neil Geeson says "Is this Hurlford Yard? Maybe a GNoS Class 21 on its acceptance Trial."

Looking at old OS maps this matches perfectly. The view is looking north and the little hut in the distance is next to the depot turntable, the shed itself being behind and left of the photographer on the opposite side of the running lines. There is an inverted 'V' shaped telegraph pole with three arms that matches perfectly with photos as do the lights. There are not many photos of the yard but conformation would be great!