Based on the design that can be seen, I'm almost certain that this is a British Pound coin (specifically Whales). There are many version of this coin over the last century, and trying to narrow it down without details is difficult. Please see the image below as a point of comparison to what I think is the obverse of your coin. The reverse of the coin also shares similarities with the 'ring with wording around it'.
Good guess, but the pound coin has only been around since 1983. Judging by the amount of corrosion on the coin, it has been in the ground at least 60 years.
Depending on the composition I have pulled zlincolns from the ground that are only a third to half of them left.