The ownership of the coin is at the centre of a dispute
The discovery of a rare 15th Century gold coin in Powys has triggered a legal row.
The coin, from the reign of Henry IV, was unearthed by contractor Shaun Bufton on 28 April while he was working on a new water pipeline in Newtown.
But archaeologists failed to return it to him.
Clwyd-Powys Archaeological Trust said it had made a mistake in not returning the coin and it regretted not having told him what was happening.
When it was minted in about 1400, Henry IV had just become king and Owain Glyndwr's rebellion was under way in Wales.
Wafer-thin, it weighs only as much as a modern penny, but is the size of a 50p.
It is known as a noble coin and would have been used by international traders, the gentry or nobility.
Shaun Bufton said he found it near a hedge on the site of a pipeline in Newtown.
He added: "A couple of gentlemen working for Clwyd-Powys Archaeological Trust took it away from me to investigate what it was."
Mr Bufton said he signed a form confirming he had found the ornate coin and was given a written promise by archaeologists would return it, but he has not seen it since.
Mr Bufton said his solicitors in Newtown had written to the trust, but he had received no response.
"I've had nothing whatsoever," he added. "I'm a bit cheesed off basically.
"I want it to be returned. It's my coin as far as I'm concerned."
The Clwyd-Powys Archaeological Trust said it made a "mistake" in not returning the coin to the finder and "regrets" not telling him what was happening to it.
The coin was passed on to the owners of an industrial estate, Ashtenne, where it was found.
Ashtenne said it knew nothing about the coin until July when the trust told it the coin could be collected. Its now in Cardiff's National Museum of Wales while the company decides what to do with it.
Mr Bufton's solicitors, Robert Hanratty and Co, said a single coin was not treasure trove so legal ownership was unclear.
David Stephenson, a research fellow in medieval history at Bangor University, said the coin was known as a noble.
"It's probably a noble from the early part of the reign of Henry IV, let's say around 1400," he added.
"It's interesting because gold coins are something special.
"Although hundreds of thousands were made they only got used by very high value people."
Mr Stephenson said not many of the coins survived.
"I think the coins tell us something and closer analysis may reveal what it tells us about the history of mid Wales at an interesting and rather mysterious time," he said.