Dr Philip de Jersey, a former Celtic coin expert at Oxford University, said the haul was "extremely exciting and very significant".

He said each individual coin was worth between £100 and £200.

The exact number of coins found has not been established, but archaeologists said the hoard weighed about three quarters of a tonne and could contain about 50,000 coins.

The exact location of the hoard has not been revealed by the authorities but Environment Minister, Deputy Rob Duhamel, said he would do everything he could to protect the site.

"Sites like these do need protection because there is speculation there might even be more," he said.

"It is a very exciting piece of news and perhaps harks back to our cultural heritage in terms of finance. It was found under a hedge so perhaps this is an early example of hedge fund trading."

It was found by Reg Mead and Richard Miles in a field in the east of Jersey.

They had been searching for more than 30 years after hearing rumours a farmer had discovered silver coins while working on his land.