Metal detectorists claim the Government could deprive them of hundreds of thousands of pounds under planned changes to the Treasure Act.

Among proposed revisions to the current legislation, passed in 1996, include redefining single gold coins as treasure upon their discovery.

Current rules state a treasure find as two or more coins, meaning single pieces do not have to be reported to a coroner, who have powers to declare them legally as treasure and prevent them from being sold.

Hobbyists insist the change could result in a drastic decrease in them cashing in on their rewards at auctions.

Officials from the National Council of Metal Detecting (NCMD) said the changes could see huge financial windfalls become “a thing of the past”.

A NCMD spokesperson said: "Extremely rare solo coins are beyond the value of even the British Museum when sold at the market price. I suspect that the advantage of them being captured as treasure is that these institutions won’t have to pay as much.

"Take the Coenwulf gold mancus, which was bought by the British Museum at auction for £357, 832 in 2006. If that were declared as treasure, the Treasure Valuation Committee (TVC) would have given it to an expert to value.”