Cool little item , tony641 .
EPNS usually stands for "Electro-Plated Nickle-Silver" .
The good news is , if you really like & want to keep this item , it can be electro-plated again (if there's plating missing) .
An alternative to polishing is : using a spoon or two of baking soda + a glass or plastic (tupperware works fine) non-metalic container + a piece of standard aluminum foil + hot water ;
Wash your item with dishsoap & a cloth or sponge , then rinse in hot water .
Add hot water to the container , mix in the baking soda & submerge the piece of foil in the container & set your item (fully covered by the liquid) upon the foil in the container .
You can also use a small toothbrush , along the way in the submersion process , to gently 'brush off' flakes of tarnish .
This should take between 2 - 5 min.
After electro-cleaning your item , wash & rinse & dry your item .
It should only take a short time for you to see a very shiny item in your hands .
I'm only suggesting this as a quick alternative to rubbin' the heck out of it with polish , and the fact that although it's a nice looking cup , it's only an electro-plated item with a small value (IMO) .
If you do decide to sell , you'll know if there's plating missing , via this method (& also have a better idea if it's intact) .
Whoops ... ironlord1963 beat me to the draw !(very slow typist here , in more ways than 1)