I'm no pushchair expert and there were a couple of people ahead of me, so I couldn't' get a close up look, but having looked at the yoyo website, I would say that the yoyo website has a nice moving image illustration of a mother folding up a yoyo with one hand (looks awesome !). So if that is how easy the yoyo is to fold, then surely that would negate the "but how would I hold the baby" claim.

However, judging by the general gist of the comments, it just seems that in all my BA miles I must have been a rare exception to not witnessing a pushchair being taken on board.

So at least now I know the practice is fine, and it was merely the passenger that was at fault - which was sort of my conclusion anyway.

Thanks all !