It's the Bolwell MK1 from 1958. Djetset made me remember!
It is indeed the Bolwell Mk 1 - a 'one-off' originally built in 1958.
Bolwell didn't really start mass producing cars until the Mk 4 (55 cars).
The Mk 2 was another 'one-off' and there were two made of the Mk 3.
You've sometimes got to be very quick after a clue is posted!