A museum prompted a bomb scare after unearthing a box labelled "bomb" in its archive.
Volunteers at Bishop Bonner's cottage in Dereham, Norfolk, found the package, filed under the letter 'B', while sorting through items held in storage.
After opening the box they found three clay balls packed with gun powder with wicks sticking out of them.
Much to the amazement of his neighbours, Bob Davies, vice-chairman of the Dereham Antiquarian Society, decided to take them home with him.
He said: "We think somebody made the grenades during the First World War in a Dad's Army-style attempt to defend the country.
"I thought they had sat on a shelf safely for 90 years so it should be ok to take them home for safekeeping.
"I called the police and they told me not to touch them. The next thing I knew, bomb disposal experts arrived.
"I think my neighbours were quite surprised."
He added that experts were so impressed by last Tuesday's find that they will find a new home for the grenades in the bomb disposal unit's museum in Colchester.