Your answer confuses me a little BOAC. ATC does not clear an a/c for "departure". However, I deduce that the "take your seats for take-off" to the c/c would only be used after having received take off clearance from ATC, thus no confusion is in fact possible. Fair enough, that explains it. I was only curious because I have flown on many different operators and only this particular one uses "take off" in its PA call.