The conditions on BA's discount CW and F fares ex-UK are harsh. Probably too harsh.

I expect that if BA kept all the existing advance purchase, length of stay, ticketing and refund conditions and made the change rule GBP 200 plus the difference in fare the outcome would be at worst revenue neutral and might even sell some seats that would otherwise go unsold.

On the other hand they would however have to explain to I-class-in-the-sale passengers wishing to change their ticket to NYC 6 days prior to departure that they have to pay the GBP 200 change fee plus the GBP 4,000 difference in fare. That may drive some people away from BA.