Note the unusual wagon and the pair of diesel shunters in he distance.
The wagon is branded 'Running and Maintenance Depot Cambridge' (note no mpd or PW department etc,) and was carrying these containers. The wagon is a 'conflat' and it looks like it is carrying some kind of tanks. If so they must have been carrying something clean like water, dry sand or perhaps some sort of water treatment chemical As if the load had been waste oil, or boiler washout slurry we would probably see evidence of it on the outside of the tank.