The JEI K1 single manual percussion keyboard
The K1 was exhibited at the Russell Hotel Trade Fair of late August 1969 and can just be glimpsed behind the J71 organ in the photo below:
(1) Its scope is likely to have been a range of fairly standard effects - as built into larger electronic organs (from the late 1950s / early 1960s) - along with a number of "Denney specials" borrowed from the Vox guitar-organ. The promotional image below seems to be the only one to have been published by Jennings. So far as one can tell, the K1 keyboard is likely simply to have been a tester to see whether a stand-alone version of the third manual of the J70 organ attracted any interest. The answer seems to have come in the negative. The K1 did not find its way into general production.
(2) The Attack Percussion unit, which evidently stands in close relation to the K1 keyboard, and for which a full-page advert was taken out in September 1969 (on this page), and , is said to be subject to world patents. The text of the review was repeated without the illustration of the K1 in "Melody Maker" magazine.
As for the patent or patent-applied for number mentioned in relation to the Attack Percussion, none seems to have been printed in any of the obvious places. Perhaps one will eventually come to light.