Originally Posted by
teledude
Oh and as this is a SYD-LHR flight will they argue about upgrading as far as SIN and then continuing to LHR in J?

If you are booked on BA16 SYD-LHR you will only be able to upgrade if there is availability on BA16 SYD-LHR. If there is only availability on the SYD-SIN segment you cannot upgrade unless you change your current booking.
If you are booked BA16 SYD-SIN (with either a stopover or connection to BA12) then you can upgrade.