Identification of a microcar of the 1950s

[luisps]

I would like to know the origin of a microcar that was photographed in Barcelona (Spain) in the first half of the 1950s. The photos show various details of the vehicle and its size compared to a SEAT 1400. The license plate indicates MTR 80627, which has no meaning to me. The engine located in the rear is a single-cylinder, air-cooled engine and appears to be of motorcycle origin.