Under the Treasure Trove Act, the landowner and the detectorist split the money. If the government wants the coins as national heritage, they have to pay fair market value as determined by a panel of experts. Amazingly, the windfall is not taxable.
Such a law would be an enormous improvement over American law.
Under American law, the "detectorist" gets nothing, the landowner probably gets nothing, and the government gets everything.
It is an amazingly stupid law in the United States.
It puts almost all the incentives on the side of breaking and evading the law.