Originally Posted by KARFA

that's not correct. direct bookings with BA can have other non BA flights in, but obviously those non BA flights would not be upgraded by the GUF.

for a TA booking there is a restriction when applying a GUF all flights must be BA ones. however that is only relevant to revenue bookings, as this is a reward booking it couldn't be a TA booking

there is some more information on GUFs in the GUF guide linked to in my signature and through the dashboard.