Most of the treasures found in England are by recreational detectorists. The laws there promote it. But, you can’t just go and trespass either.
Hopefully some families will look online and find the rules. I think it is as simple as show up at a farmer’s house, have a written “contract” that says if any treasure is found, the government will be notified, and if we get to keep the treasure - the farmer gets XX percent of it. (I imagine there is a typical percentage). If I was a farmer seeing mom, dad and a couple of little kids in their rubber boots - I would be happy to let them on. (As long as the contract has something about they can’t blame me if they get hurt on my property!”.
In England, if you find a bunch of mundane treasure (like roman coins, gold bars, etc.) you get to keep it. Stuff that is notable and would be helpful to the archaeologist or a museum, they have to pay the finder the value of the artifact.
I think it’s a great idea. Better than the guy in the USA that posts some cryptic poem about the treasure he’s buried.
I’m not British and I’m not a barrister, but I believe things found in the ground can be declared ‘treasure trove’ by the local coroner. If something was simply lost, it belongs to whoever found it (and/or the landowner). But if it was hidden or tucked away to be fetched later it is treasure trove and belongs to the crown. But in this case, the government plays fair. Anything that is historic is turned over to a local or national museum and the finder/land owner is paid a full, fair price. Anything that museums aren’t interested in are returned to the finder/land owner who can legally sell them on the open market.