Sinclair had, it seems, a design tradition that oddly mirrors Apple's. Lots of brilliant prototypes, and I hope the Delete book, which is where I first saw this, hasn't exhausted the treasure trove.

You may be interested in Rick Dickinson's Flickr account which contains the prototypes he developed while at Sinclair:

https://www.flickr.com/photos/9574086@N02/albums

Mostly Rick Dickinson, who was a superb industrial designer.