A rusty iron helmet that may be the only surviving relic of one of the most decisive battles in English history has been found in an antiques shop.

A label on the helmet suggests it was fished out of the River Derwent at Stamford Bridge, where King Harold Godwinson defeated Viking invaders in 1066 before he was beaten by William the Conqueror at Hastings.

Historians speculate that Harold, England’s last Anglo-Saxon king, may have halted the Norman Conquest had he not had to fight at Stamford Bridge, near York. He not only had to beat the 10,000-strong Vikings, but march to Yorkshire and back at a punishing pace.

The Vikings had invaded in pursuit of the English throne, but Duke William of Normandy also claimed it, on the grounds that Harold Godwinson, his cousin, had sworn him an oath of fealty and thus should surrender England to him. The Viking force, estimated at 10,000 men, was ready first and had already landed and defeated the northern earls at Fulford in Yorkshire. Harold marched his army 180 miles to Stamford Bridge in four days to take the Vikings by surprise. In a fierce hand-to-hand fight at the bridge over the Derwent, Harald Hardrada was killed, his army shattered, and hardly a tenth of the Viking ships made their way back to Norway.

It was believed that no relics of the battle had survived. Nicholas Reeves, an Egyptologist, found the conical four-plate helmet by chance at a Midlands dealer’s. “The label says ‘Viking Helmet found in the River Derwent at Stamford Bridge by D R Lancaster, May 21, 1950’,” he said. “The possible significance of this was quite unrecognized by the seller, and even the helmet itself appeared to him to be of only moderate interest, presumably because of its condition.”

Alan Williams, a medieval armour metallurgist at the Wallace Collection in London, concluded that the metal is a low-carbon iron typical of early artefacts from Celtic times to before the Industrial Revolution. “It could be 11th century, or Roman, or Civil War,” Dr Williams said. “The shape suggests an early medieval date, and the 10th-11th century helmet attributed to Saint Wenceslas is also a low-carbon steel so it could be 11th century, but we cannot say positively.”

The mystery over the helmet’s origin is likely to persist unless someone is able to identify the label’s writer. For the moment it remains in secure storage, but Dr Reeves said: “If it’s what I suspect, then it belongs in a museum.”

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