I forget what % goes to the Crown but I remember it is really high
Still, Maybe a higher % than you might get in the USA if you let yhe fbi know you found a bunch of gold
The law regarding “treasure” in England is, the value is set by a third-party committee, and half goes to the finder, half to the land owner. Apparently, there are few disputes over the valuation.
Of course, they do have to pay income tax.