For the purposes of this answer, I have assumed that you are (i) BA Exec Club, (ii) UK resident and (iii) have access to the BA mileage.

If you have 100,000 BA EC miles then this is what you need to travel on any of the partner airlines in 1W between UK and Australia. You have the options of all of the carriers. Your problem may be getting a seat at some times of the year. I did a mixed BA out with a QF/CX back last time for the standard BA mileage price.

I have hundreds of thousands of QF miles that I am trying to use on QF for LON-Australia but can never get a seat on QF. This week will see me trying to get a seat on any other carrier via anywhere. QF sometimes allow you to go WTP if you are booking on a BA flight. For example, I was offered BA LON-LAX and then QF LAX-SYD with the BA in WTP. However, I really needed a business seat as it was straight off the aircraft and into a meeting both ways on the trip.

I hope that this helps, happy landings and good luck with availability.

spotwelder