Nicely put

One almost has visions of BA calculating the fare for a passenger and then, at the last minute, saying .... “oh, we’ve just been told by an outside party that we’re legally obliged to add some sort of special supplement .... really sorry about this ..... totally out of our hands of course”.

In fairness (maybe not quite the right word), BA are far from alone in this unwelcome practice. Even the likes of Emirates have long been playing the same game ; not least for straight redemptions, where it can in some cases be cheaper to just buy a cash ticket rather than give up miles too, for an (ahem) ‘award’ flight.