An edition of the Magna Carta which was collecting dust in a council's archives could be worth £10million.
Historians have hailed the discovery of the version of the historical parchment as an important find after it lay forgotten in the history department of Kent County Council.
The document, which established the principle of the rule of law, was found in archives kept in Maidstone but which belong to the town of Sandwich.
It is one of just 24 editions of the Magna Carta known to exist around the world.
Professor Nicholas Vincent, of the University of East Anglia, who authenticated the document, said the fact Sandwich had its own Magna Carta supports the theory it was issued more widely than previously thought to at least 50 cathedral towns and ports.
He added the discovery gives him hope that further copies will also be found.
He said: "It is a fantastic discovery which comes in the week that the four other known versions were brought together at the Houses of Parliament.
"It is a fantastic piece of news for Sandwich which puts it in a small category of towns and institutions that own a 1300 issue."
"And it is very likely that there are one or two out there somewhere that no one has spotted yet."
Prof Vincent, who specialises in medieval history, went on to say the value of the Sandwich edition could be up to £10 million, but it was ripped with about a third missing.
He said: "This would be an upper value as it has, like the town of Sandwich, suffered over time from French invasions and the like."
The discovery was made by archivist Dr Mark Bateson at the end of December just before the 800th anniversary year celebrations of King John's concession.
It is understood that Sandwich does not intend to sell its Magna Carta but instead is hoping to benefit from its potential as a tourist attraction.
The town's mayor Paul Graeme said: "To own such a document is an honour and a great responsibility."
The first Magna Carta was drafted by the Archbishop of Canterbury and agreed by King John on June 15, 1215 to make peace with a group of rebel barons. It was reissued and reaffirmed on many occasions in subsequent years.
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