A Viking's penny pendant is found near King's Lynn

The silver penny was hammered into a pendant with the cross facing outwards

A St Edmund memorial penny worn by a Viking to "advertise his Christianity" has been found by a metal detectorist.

The Anglo-Saxon king was killed by the Vikings in AD869 and made a saint shortly afterwards.

Numismatist Adrian Marsden said the pagan Vikings went from killing Edmund to "striking coins in his name" to wear as converts within two generations.

The AD890-915 silver coin was found at Congham, near King's Lynn. Norfolk Coroner's Court declared it treasure.

This hoard of King Edmund pennies was discovered at Worlington in Suffolk - they are smaller than a 5p coin

"St Edmund memorial pennies were struck by Vikings who [had] become Christians so the wearer could advertise his Christianity," said Mr Marsden, from the Norfolk Historic Environment Service.

"In the AD910s, around the time this coin was struck, you've got King Edward the Elder moving east and north to reconquer East Anglia, which the Vikings held since they did-in King Edmund."

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The Anglo-Saxon Chronicle described how Scandinavians formed a Great Army to raid, conquer and winter in England from AD865.

They fought and killed King Edmund, whose body was laid to rest at Bury St Edmunds, Suffolk.

A Thor's hammer found just outside Thetford and currently on display as part of a Viking exhibition at the town's Ancient House Museum

Metal detecting and the law

• No search can begin until permission has been given by the landowner

• All finds belong to the landowner

• Any find in England, Wales and Northern Ireland that is more than 300 years old, made of gold or silver, or found with gold or silver artefacts, could be treasure under the 1996 Treasure Act

• These must be reported to the appropriate county finds liaison officer

Source: Portable Antiquities Scheme

Once Alfred the Great defeated the Great Army at Edington in AD878, the warlord Guthrum retreated to East Anglia, where it was ruled under Scandinavian law and customs, known as the Danelaw.

Yet within a short time, silver pennies were being struck in Edmund's name, possibly encouraged by Guthrum who had been forced to convert to Christianity.

"While they may have become Christian, they still have to be reconquered by Edward the Elder, son of Alfred the Great," said Mr Marsden.

"So you perhaps get a Viking, whose father might well have worn a Thor's hammer, who's a Christian wearing a coin with a cross to convey that fact - this pendant's got quite a story behind it."

Norwich Castle Museum hopes to acquire the coin.

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