I don't think the offer works for BAH - given you can get more Avios now by buying a few bags of carrots in Sainsbury's than on some flights, it's difficult to see how doubling up will drive bookings. People will sign up and take what they get, but no-one is going to go up a fare class to get a tenners worth of Avios.

I do feel that the world of Avios collection has changed very profoundly and as stashes deplete we'll see this beginning to become very obvious.