After talking to several people (off the list) the present assumptions are summarised as follows:
It is Caithness - but likley not Colin Terris.
It is neither Alastair MacIntosh nor Helen MacDonald.
It is Helen's cutting design, though - and therefore likely facetted by Martin Murray.
The entire weight might be Martin Murray.
Could be a design study (not selected for production), an event piece, or just a 'homer'.
Any further comment would be appreciated.