Forgot to add,

to CCF :)
You may try posting this on TreasureNet in the "Finds" forum, as well as here on CCF's own Metal Detecting forum, there are a good many detectorists here and there from NE who may be able to recognize it based on type and/or size.
2mm and 26-30mm is quite large. The age, wear, and encrustation screams 1600-1800 to me. This may also very well be a medal or token, of course.
I do not think it can be conserved much; even a long soak in olive oil and careful cleaning is not likely to reveal much further detail, but you can always try. I would recommend soaking it in Verdi-Care in the meantime to stop the verdigris and then sealing it with Ren Wax.
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