A couple pottering about in their vegetable patch have dug up what is believed to be a relic from the English Civil War.

The rarity is a 4lb cannonball, which experts say could have been fired during the siege of Witton Castle, near Bishop Auckland, County Durham, during the 1640s.

Teacher Linda Bentley unearthed the cannonball, which is the size of a cricket ball, while planting lettuce in the garden of her new home at nearby Witton-le-Wear.

She and her husband, Michael, a university lecturer, have handed it over to the local history group.

"It has proved quite a find," said Mrs Bentley, "and there seems to be quite a story behind it."

The cannonball was originally found by keen gardener Stephen Binks on his allotment at Witton 40 years ago.

He took it home, but his sister Margaret became alarmed and threw it over the fence into a field. It landed in a patch of nettles.

"Apparently, she thought it was a bomb," said Mrs Bentley.

It lay there until the Bentleys decided to convert part of their garden, which was the original field, into a vegetable plot.

"I got quite a shock when I dug it up," said Mrs Bentley.

Kelso Yuill, a member of the recently formed Witton-le-Wear History Group and a collector of military memorabilia, believes the cannonball is a relic of the siege of Witton Castle.

"We know the castle was under siege for a short time in the 1640s and the village of Witton would have been an ideal spot to launch an attack on the castle, which was then in the hands of the Darcy family."

It was likely that the cannonball was fired from the castle.

"The 4lb balls had a range of 1,400 yards and the cannon would take four horses and 20 men to pull it."

Mr Yuill said it was very rare for a Civil War cannon ball to be found in an area like County Durham because there was very little conflict there.

l The Witton-le-Wear History Group is appealing for more information about the siege of Witton Catle and the cannonball, which is now part of their archives. Contact Kelso Yuill on (01388) 488376.