Is there someone hanging onto the handrail and speaking to someone (the guard?) who is leaning out of the leading vehicle (presumably a brakevan)? I wonder why, and also who are the other people standing opposite the third carriage?
The train is about to reverse and change engines, which would account for the people.
Can anyone tell when the photo was taken? The stock certainly looks pre-war, whilst there seems to be quite a bit of SR concrete in evidence supporting the signal cables and possibly the Peek Freans advertising hoarding.
Other clues:
1. the stock is early Maunsell (and mostly 1st class - 7 compartment) and has just Southern on the side, so mid-30s onward, 1950 at the latest.
2. the signals are SR not SECR, and don't match the 1919 diagram on the SRS/Signalbox sites; the alterations may well have happened in 1930 when the small "B" box at the tunnel mouth was abolished.
3. there is housing faintly visible in the left background. Maps show the area being "developed" in the 30s, but I can't quite locate the ones on the map; as a wild guess, are they in fact prefabs, which would date the photo late 40s. Does anyone know that part of Folkestone (Dover Hill)? Otherwise 1935-50 is the best I can do.