Thank you all for your input. I am sure I saw the building in the background of the Tv program standing quite alone near the cliff edge. Turns out I did not record the program but while watching it I did write down the part of the walk where the structure was- on the South West Coast path between Fowey and Polperro. The link Little Nell provided is the program I saw, about Cornish Smugglers. Tony Robinson paused while on the path to tell a little story and then as he walked on the structure was in the background looking very similar to that in the portrait. I don't think the portrait is of Popham. This Watson family were cousins of Sir William Henry Watson who was brotherinlaw of Lord Armstrong of Cragside. Watson family portraits belonging to this branch, and previously in the possession of Joseph Yelloly Watson (1817-1888) are now at Cragside.
