Thank you Hose_dk for your insights. I am now nearly 100% sure maker is ‘TORNBERG’. Since deciding the maker is Tornberg I found an auction house selling nearly identical spoons as marked Tornberg, LinkÃ¶ping from 1811-1833. Is it possible the city is LinkÃ¶ping not NorrkÃ¶ping?
LinkÃ¶ping might make some sense as my family is actually originally from there (a long time ago).
Marks on the spoon in question falling into place…http://putfile.com/pic.php?pic=5/14913202786.jpg&s=f5
Thanks to all who have had a look.