Originally Posted by heartybob

Where did you see this option in MMB - is it the "Upgrade for cash" option or something similar - and if you select it, what bucket does the upgraded ticket book into?

This is exactly the same wording as appears on the price quote page for a new booking when ba.com offers to upgrade a cheapest inflexible J class (R) to more flexible J class (e.g. D) before payment (increase ticket flexibility option).