I met John Grant in Cambridge about 10 years ago at some event, he's a really nice guy who can tell very interesting stories about the early microcomputer industry in Cambridge and his later hardware projects.
Another interesting thing – the CPU used in the Spectrum prototype shown in the linked article is a Z80A made by SGS-Ates (a predecessor of SGS-Thompson). I've never seen a Z80 made by them and had to look up the logo, but they started second-sourcing the Z80 in 1979 according to (sorry, page in German) https://www.homecomputermuseum.de/sammlung/detailansicht/com.../
Another interesting thing – the CPU used in the Spectrum prototype shown in the linked article is a Z80A made by SGS-Ates (a predecessor of SGS-Thompson). I've never seen a Z80 made by them and had to look up the logo, but they started second-sourcing the Z80 in 1979 according to (sorry, page in German) https://www.homecomputermuseum.de/sammlung/detailansicht/com.../
Here's a link to the logo: https://www.elnec.com/en/support/ic-logos/manufacturer-descr...