Knaresborough has its share of mysteries — did Mother Shipton really predict the future and how did Blind Jack build so many roads?

Now there is a new one: how did a First World War bomb lie undiscovered in the River Nidd for so many years?

The bomb was found in the shallows beneath Grimbald Bridge yesterday by litter picker Simon Briscombe.

Mr Briscombe thought it was a gas canister until the bomb squad turned up and carried out a controlled explosion in a nearby field.

It seems miraculous that such a weapon could have lurked undiscovered for more than a century — and how did it get there?

Intriguingly, Kathy Allday, chair of Knaresborough Museum Association, said a British plane came down in the Nidd during the First World War, close to the area where the weapon was discovered.

The pilot was killed and debris was scattered across the river. Could it have been carrying the bomb?

Unexploded shell in Scriven Park

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Mr Briscombe, who stumbled across the weapon, thinks this explanation is plausible. He said:

The self-employed electrician said he hadn't managed to do much work today but was grateful to be alive.