When we moved into our old house in Crown Drive many moons ago (we used to back on to Millburn Academy), we noticed that our garden wall wasn't flush with the others that backed onto the school. After tackling a wasps nest and tearing down the remains of the rear wall, my father found a hand grenade in the foundations.
We called the police, and an officer duly came down to inspect it and, after a couple of calls, picked it up, put it into his cap on his passenger seat, and drove off.
A few weeks later, my dad bumped into the same officer and asked what happened next. Apparently, the bomb disposal squad came down to the police station, looked inside the safe (where it was being kept), and refused to remove the grenade. They unbolted the whole safe from the police station, and blew the whole thing up in a controlled explosion!
We later found out that the land where Millburn Academy now sits *may* have been used as a training site for the army, and that explains why this ordnance was found there.