The shop was evacuated as a bomb disposal squad was called in to deal with the WWII weapon.
The grenade was handed in with a box of toys. "I don't think it was given with malicious intent," said a Barnardo's spokesperson.
Another charity shop had an altogether more pleasant surprise last week when it received an oil painting worth £25,000.
The painting, part of a collection donated to the shop by a mystery benefactor, was handed into a St Rocco's Hospice shop in Warrington, Cheshire. A volunteer at the shop noticed that it was by celebrated Scottish artist Francis Campbell Boileau Cadell and had it valued at a London gallery.