I'm fairly certain that this item (and it's kin) are silverplate. However, after spending hours looking through 1000's of patterns I cannot seem to locate the country of origin, the maker, or when it was made.
It's Norwegien silverplate. The 'NM' stands for 'Norsk Mønster' a design copyright mark used in Norway, and the 'GP' stands for 'Gullsmed Plett', silverplated.
Thanks for the information. However, I am still unable to locate any more information about this pattern. Nor can I decipher the date marking. I don't imagine that these items are very old - mainly because of the single die striking of the hallmark. My curiosity has the better of me at the moment.