Actually the UK government has a very good system for compensation of found treasure. I’m not sure of the details, but my husband knows, and maybe I can get him to clarify later.
That's the smart way, if they ever want to have artifacts actually turned in for scholarly study or display. It'd be smart too, to make the price for an artifact to be significantly -more- than the commodity price for the metals, to keep people from just melting stuff down and selling it privately.