When the sleeper train is departing the station, the sequence of flags and whistles is out of step with the signals being shown. The staff and guard would not give the signal to depart until after the signal had changed to green, and only when the signal changed to green would the "OFF" indicator light up.
Also at night, a green lamp would have been usually been used rather than a green flag.
Also at night, a green lamp would have been usually been used rather than a green flag.
The text on the warning poster behind Jim in the sleeper berth is gobbledegook placeholder text; albeit in the correct British Rail font.
As the train is about to depart, the cameraman's shadow is clearly visible.