I’m currently looking at options for SYD/MEL (from London) next year which will let me use a GUF to upgrade into PE or CW using T or I revenue class availability. I class availability on BA16 ex SYD is scarce, so looking at BA-ticketed routes that use CX or QF for the first leg to HKG or SIN (which I know the GUF can’t be used on), and picking up an upgradeable seat on BA metal to LHR.

For many of these options, EF shows good I or T availability for HKG-LHR or SIN-LHR legs but when trying to book on the BA website the selling class shows as a higher PE or CW bucket for the same flight.

When looking at applying a GUF, does the selling class being offered for a particular routing matter, or is the availability of a T or I class for the flight as a standalone leg enough to be able to get the upgrade?

Thanks!