Some say Rebekah Wade. Bare knuckle boxer, editor of the Sun and now Gordons' speechwriter.
"It was during a dinner the night before Brown's speech in Manchester," I'm told. "Ed Balls muttered it while we were chatting about Cameron. No one picked up on it except Rebekah, who quite rightly thought it was dynamite and suggested he might want to get it into the speech quick-smart.
"Ed, like a loyal little terrier, duly scampered off back to his master with his tail up and the rest is history."
Wade has so far refused to take credit for it, unlike Alastair Campbell, who has boasted about coining some of Tony Blair's best soundbites.