Awesome! And here it is : spectrumcomputing.co.uk/entry/5691/Z... The site lists a ZX81 version too, but it doesn't seem to be archived. Did that exist?

Yes, he wrote multiple games for the ZX81, some excellent ones in fact. (Such a limited platform is ideal for one person working alone.) Probably also published by Work Force - I think they are lost in the mists of time now, although there may be some tapes in the garage somewhere!