On a mineral train, the train is travelling on the Down Main line and could have been heading for the Berks & Hants route although the way the exhaust is lying could be indicative of a speed in excess of 40mph, which was the maximum speed of trains heading for the B&H at this point. In all likelihood there must have been sufficient time to run this train along the Main line (the relief line being otherwise occupied, maybe). The adjacent line in the picture is the Up Main and wasn't bi-directional in pre-Reading panel days