I dont follow - is there a reason why he would not want to disclose a freshly dug find?
Anything dug up after September 24, 1997, that is 10% or more metal and 300 years old or older belongs the government per the Treasure Act 1996. Some of the verbiage:
Where objects are found to be treasure, they belong to the Crown, unless a third party has been granted the right to treasure (called a "franchise") found in a particular area (a list of some such franchises is at pages 244-251 of Hill). Usually the national museums are involved (in England the British Museum, in Wales the National Museum of Wales). They provide expert evidence and guidance to the coroner. To encourage the reporting of finds, the finder is invariably rewarded with a payment representing the value of the find. etc etc etc
Treasure handed down from family you get to keep more of.