The chariot description is the giveaway, do an image search for that. Civil Defence and fire service use, not uncommon, nice unit, but normally found behind Austin K2 Fire Tenders I think, here you go;
http://hmvf.co.uk/forumvb/showthread...ax-AFS-trailer
See the chariot similarity? You would find these Commonwealth-wide, for sure, and I think the design goes back before 1939