This question turns up at regular intevals at all the photography forums!
These lenses are what I call the "British" series. In 1985, the British arm of Carl Zeiss Jena acquired the blessings from Jena, to market a series of Japanese-made lenses under the Carl Zeiss Jena name, the zoom lenses all shared the name Jenazoom. They were sold as another independent label series of lenses, back by the British firm.