I've inadvertently stumbled onto the correct identity for this chair and solved the mystery.
It was a bit weird really as I was looking for something completely different - I was searching for interesting 70s and 80s gadgets for the latest speed modelling challenge and an image of the chair popped up during a Google images search:
Chair F978.jpg
@unknownuser said:
Chair F978
Geoffrey Harcourt, 1935, London, United Kingdom
Year of design - 1968
Manufacturer - Artifort, Netherlands
Materials - Structure polyurethane foam upholstered in Super Bultex, base consists of a painted aluminum disc
Dimensions - L70 x A69 x C75 cm
The F978 chair was designed by Geoffrey Harcourt em1968.
The structure of polyurethane brown and round base in lacquered aluminum in brown are the main features of this model. The chair is upholstered in woven wool-colored orange.
Harcourt has won many awards during his career and in 1978 received the title of 'Royal Designer for Industry.''
Source: www.zeppelinvintage.com
Best of all, it still appears to be in production: www.artifort.com/en-gb/collection/fauteuils/page_product.aspx?id=1424