Naturally, in GB as in all socialist countries everything belongs to the state.
They do pay the finders the value of the “treasure” they turn over. Some folks have gotten rich by their finds. If they find the “treasure” on another person’s property, they are required to pay part of their award to the owner, which is only fair. The process has seen a larger number of people turning over their historical finds so everyone eventually gets to see them, instead of them wallowing away in someone’s private collection. It’s also given archaeologist’s, etc., an opportunity to add to the history of the country and the people who inhabited it at one time.