This is the first of the Mamod Minor range, introduced in 1939, with the flat base, disc crank and single wick meths burner.
It is an overtype engine with everything mounted on top of the 1 1/2" diam x 3 5/8" boiler, including the 1/4" diam x 1/2" stroke cylinder, 1/4" safety valve, 1 3/16" diam disc crank and the purely decorative chimney. The disc crank has the name Mamod Minor engraved on it.
It appears to be in good condition, although the base looks as if it has been repainted at some time in the past.