Sorry, I don't honestly know. What I do know is that if you use the BA app to check-in, or if you request a boarding card in the app once you have checked-in, your digital boarding card in the app will have the "fast track" QR code on it, if you are entitled to use it. Otherwise, if you are checking a bag, they will tell you at the check-in desk without you having to ask them (that has been my experience, anyway).