I find it pretty amazing that there's a built-in mechanism at BA to evaluate these situations (ie. bringing it up with the CSM/CSD for discussion/negotiation) as if it's the norm and that people on this board experience this all the time (whether by witnessing others doing it or being the ones inviting "guests"). The idea of bringing in extra bodies into the F cabin is especially striking considering how many legitimate passengers BA squeezes into its F cabin to begin with (and compared to other airlines). I have flown F with BA many times and thankfully don't remember witnessing this. The protocol should be very simple, unless there's some emergency, "no" or the F passenger should go to the back.