Fairthorpes live right on the line -- almost too big to be classified as a minicar -- but considered small by the drivers of most other sports cars.
The early versions of the Electron Minor were fitted with a Triumph 948cc engine. The same engine that was used in the Triumph Standard Ten (also referred to as the Triumph Sedan). Later versions were bumped up to the 1147cc engine that was standard in the Triumph Herald. Along the line several Ford engines found their way into Fairthorpes, and the run ended up with the engines used in Triumph Spitfires.
(The Electron was something altogether different -- fitted with a 1098cc Coventry Climax engine -- making it a strong competitor on UK tracks in the late 50's and early 60's.)
But both of these cars have a common ancestor -- the Fairthorpe Atom. A fiberglass microcar that sported engines such as an Excelsior two stroke, a BSA 250cc and a Gold Flash 650.