Story I read ages ago somewhere...
In among all the university buildings on Oxford Road in Manchester is (or was) the National Computing Centre. It was a fairly high profile building and an occasional target during the Troubles in the 70s and 80s. One day someone went past, dropped a bag full of batteries and wires, and ran off. They called the police and got the bomb squad out. After a brief investigation they were allowed back in. It wasn't someone trying to blow the place up, but a shoplifter who had nicked a load of stuff from Maplin just up the road.