Were your bags checked right through from the UK to Oz?
If so it is the responsibility of your last connecting airline to sort out the mess even more so if it was a BA/Qantas codeshare.
My bags were lost in Madrid on a flight from EZE with Iberia,they had been checked right through to GLA with a BA flight from Madrid.
BA did the tracing for us even though it wasn't strictly their fault.
I had hoped an expert would have replied to your post by now.