Surprisingly, I came across a photo of another Hydro Bug just yesterday that had been on the forum a while back.
I have found no further information beyond that it was made in the 1970’s by a company owned by Jack Wilderspin Ltd, High Street (or possibly College Farm), Fen Drayton, Cambridge.
There’s reference in The Grower magazine in 1977 to the Hydro-Bug along with a machine called the Jack-Truck.
Jack Wilderspin, being a local engineer, also made the Jack-truck which aided the loading of pallets. There is no reference as to what the Hydro-Bug was intended for.