Originally Posted by Bukhara
It appears that you can amend a GUFT booking until 24hrs before departure of both outbound AND inbound flight, and retain your upgraded cabin. The GUFT is lost if you cancel/amend inside the 24hr window. The amendment will, of course, be dependent upon the availability of I class if you have booked through an agent or U class if you booked directly with BA.
Can I just clarify. Are you saying the a GUFT booking becomes flexible, as you have outlined, even if the underlying fare (eg T class) is restricted and does not allow changes? So a GU undoes the inflexibility?