Top, Medallion found by Caroline Bird 24 February 2018. It was in a field north of East Road in East Mersea. The date on the coin is 1550.
Chris Wheeler provided the lower images of a similar medallion, and said "It is a Jetton. The 'M' is the mark of Margareta Van Oostenrijk who was an Austrian Governor of the Netherlands in the early 16th century".
From Facebook Mersea Locals.
Date: 24 February 2018