The Martin Special, built between 1930 and 1934. Based on a Rover 14/45.
That was quick! I think I gave you too many clues
. Well done, that took a lot of work.
In 1969 when this photo was published the car still existed. It was registered BPK40. It was based on the Rover with the chassis cut in half, and the rear part upturned to provide an underslung effect. Wheels hubs and axles were from a Delage. It was severely damaged in a road accident in 1935 when being driven by Tim Carson (of VSCC fame) and the builder sold the remains to somone else who rebuilt it.
The photo was submitted by Graham Facks-Martin of Launceston, Cornwall, but I'm not sure whether the builder lived in that area.