There’s a discussion of the law of treasure or treasure trove in Britain at an archaeological site here. The problem with law in this area is making it strict enough, but not so strict that no finds are reported. This is a question raised by the Sky Disk. Was the Saxony-Anhalt law too restrictive? The law on this point in Germany varies from Land to Land, in Britain from jurisdiction to jurisdiction.
Before 1996, treasure trove meant items of gold and silver that had been hidden by an untraceable owner. It belonged to the Crown, but the finder would usually be paid the full value. Coroners, as the officers of the Crown, were responsible in treasure trove disputes and are still responsible for treasure.
According to the article mentioned above, at the Current Archaeology site:
bq. Why then was the English system so successful? The first, and most important aspect is that it is limited – limited only to gold and silver (and now some bronze coins). This means first that it can be policed: the British Museum tries to track down all finds of gold and silver and is remarkably successful in its endeavours; yet this would be quite impossible if they were to try to track down all archaeological finds.
bq. It also means that the vast majority of finds made by archaeologists fall outside the system: and the local archaeological society and independent archaeologist can pursue their investigations without officialdom breathing down their necks (as happens in Scotland: which is one of the reasons why there are few active archaeological societies in Scotland).
The Scottish system is different, and so is the new English system (actually for England and Wales and Northern Ireland) under the http://www.hmso.gov.uk/acts/acts1996/96024–a.htm#1.
I just learnt a new word – detectorist. Two of the Saxony-Anhalt defendants are detectorists – people who use metal detectors. Here’s a detectorist contract.