Interestingly, it wasn't actually written for Mastermind. It was actually a stock piece of music written for TV dramas and it had been lying around for a couple of years before Mastermind began. So it's quite possible that somewhere in the archives is a scary drama from c.1971 in which the bad guy stalks the good guy to the accompaniment of "Dah Dah Dah-DAHHH!".