The finder of this coin wished to remain anonymous but I was asked to provide a full ID and a valuation.
The coin is a Charles I halfgroat, which was struck at the mint in the Tower of London when it was under the control of Parliament. It’s an example of type 3a3 with an inner circle on both sides. The mint mark isn’t altogether clear but will be (P) or (R). In the Standard Catalogue this type is listed as number 2833.
The flan is a bit irregular, there are faint scratches on the obverse but the coin is otherwise in about Fine/Fine condition. In its present state of preservation my price range would be £12 – £15.