Originally Posted by
cgtechuk
If it is the return you are looking to change many of BAs Fare Rules say that if you change the ticket after the first leg has been flown it uses historical pricing and not the current pricing so if there is availability in your fare class in this case you would just be the change fee only
If the initial fare component is unchanged, as in this case, historical pricing will be used anyway. I suspect the additional cost is down to availability of fare class.