I found an article on this little homebuilt three wheeler in the December 1986 issue of The Classic Motor Cycle, it had apparently also appeared in the December 11 1947 issue of Motor Cycling when it was already 27 years old.
The builder, a Mr. J.A Mills of Mansfield, England, built it immediately after WW1 when new vehicles were difficult to buy. The frame is steel tube, brazed together, the body is plywood built in three parts, lower "hull" with hood and upper tail added and bolted to the frame. The motorcycle based powertrain features a side valve AJS V twin which by 1947 had travelled an estimated 10,000 miles. A quick Google shows it's still around as of 2013, nearing 100 years of age.