The finder of this coin wishes to remain anonymous. I was told that it was found during 2019, which was a lucky period for the finder as this was his third gold item for that year.
The coin is a group B gold unite (twenty shilling piece) of Charles I. On the obverse there is an attractive bust of the king with XX behind. On the reverse is a square-topped shield of arms with a crown above it. The mint mark on both sides is a plume. All this adds up to the coin being struck at the Tower mint during 1630-31.
Twenty shillings was a very large amount of money to lose during the 1630s. A highly skilled craftsman might earn around ten shilling a week and unskilled works half that amount. However, those people might never have a gold coin in their possession during their entire lifetime. I believe that anyone who was rich enough to have a large gold coin in their possession could probably afford to lose it.
In the Standard Catalogue unites of this type are listed as number 2688. The example featured here is quite attractive but the flan looks to be slightly uneven. The obverse would grade about VF but the reverse isn’t as good, as the imagery in the shield of arms is weak in places. In its present condition a likely pre-sale auction estimate would be in the region of £1,200 – £1,500.