LOL at this, which was just on our local news. I'm sure it's not the first time it's happened either (I think there was something similar in 2CVGB News years ago): -

EDIT: The link doesn't work, so here's the text: -

Suspected hand grenade actually car part - but real bomb found nearby
Monday, July 06, 2009, 09:07

AN object dug up on a Derby building site and believed to be an unexploded Second World War hand grenade turned out to be an old car part.

But in a bizarre twist, members of the bomb squad called in to examine the item later found an actual hand grenade at the same site.

The suspected bomb was discovered during digging at a housing development in Alfreton Road, on June 26.

The police and the bomb squad were called in on Monday, June 29, after a site worker said the object looked like a bomb he had seen on a television programme.

They confirmed the item was actually a suspension sphere from a Citroen car, possibly left over from a former Citroen dealership which used to be located on the site.

what am i looking at?

I've heard this before, I seem to remember reading it in the Sun (must be true then) a while back!