Thanks for the suggestions (and table, Irishguy!) but those IAG figures are (I believe) the number of seats occupied on flights total during the year, not the number of separate human beings who occupied those seats. In other words, if the average flier took 3.7 flights in 2012, then BA carried 10,000,000 different human beings at least once in 2012.
It's that latter number I'm trying (unsuccessfully) to find, the number of discrete humans who fly BA in a given year. Maybe that is the "passengers carried" number, but I don't think so.