This morning the BBC news warned me that my part of the Northern Line was suspended because of "overrunning engineering work." However, it seems that "overrunning engineering work" was a bit of a euphemism. I subscribe to a tube alert SMS service and the message I got from that was a little more honest.
SEVERE DELAYS: Nrthrn from 7:16 - an earlier track search for a missing member of staff
That's a classic!