Going back to RoarAhead's situation - I think it is worth querying the Infant price again. According to the BA website "Infants travelling without occupying a seat pay only 10% of the ticket price (one infant per adult)." Your ticket price was £1,695 (I assume £200 of this is taxes). You can see from a dummy booking that the taxes for your son should be £92. So your son's ticket should be £149 + £92 = £241.

So...phone up again. Explain the logic and ask for it to be escalated to the fares department for them to double check as it contradicts the website. If you wish to embellish, consider mentioning that you are a journalist - you are certainly reporting on this board. Lets see how you get on this way.