Found this one while researching one of faksta's puzzles this morning - not surprising really as I think many puzzles are solved that way.
The car is the Harbinson Special built by Robert Harbinson in 1951.
He created a one-off sports aluminium body and mounted it on a Singer Nine Bantam chassis.
The car was built for his own personal use.
As a short postscript, Harbinson left the UK in 1954 bound for Minneapolis in the USA. On his stopover in New York he was tracked down by Gordon "Tippy" Lipe to construct a sports body and install a Porsche engine in Lipe's Cooper.
This car - Cooper Mk VII chassis no.5 - is well known today racing in Historics driven by Cameron Healy (it was also a recent puzzle on this site).
The whereabouts of the Harbinson Special are unknown since an article appeared in Motor Sport magazine of January 1954.