Trojan Mini-motor

Drawing by artist Tony Lofthouse

The Mini-motor was a postwar Italian development. Vincenti Piatti had designed a 50cc two stroke stationary gas engine which he adapted for bicycle use.
  Trojan In England, makers of small utility vehicles saw the commercial possibilities, so acquired a license to manufacture them in England. Apparently in the next few years over 100,000 were sold. Full story here.