After a very quiet couple of hours detecting this afternoon I was chuffed to find this silver coin.
It is a Groat of Edward III of England. For a long time the only coin available was the silver penny. If you wanted to spend half a penny or a quarter you literally cut it up. The value was linked to the intrinsic value of the silver.
This is a Groat or "great penny" worth fourpence. It dates to between 1351 and 1361.
You might be able to make our "CIVITAS LONDON" on the reverse which tells us it was minted in London. The legend outside that on the reverse reads "POSVI DEUM ADIVTOREM MEUM" which means "I have made God my helper"
Nobody has seen this coin in 650 years.