Thanks pmh-74 for that research. On another forum somebody posted this "A guy I work with now used to look after a maintenance depot up in Cumbria and also a fair chunk of the West Coast Main Line. He was telling me they had a dedicated fleet of wagons to shift something corrosive - can't remember. Someone in the commercial department decided (even after being warned by my pal) that they could make more money with extra wagons. Any old wagons. Come the rainy day and with open trucks, the train took out nearly 100 miles of track circuits rendering the signalling useless, before someone realised what was happening." I would think that could have referred to our wagon as being part of the "Dedicated fleet" in the 70/80's.