Having spoke to what seemed to be a more "clued in" agent at BA, I was informed that due to changes in ticketing arrangements with Qantas, BA could only access their "flexible fares" and that I should try to speak to Qantas to see if they can do an infant only booking for me on a cheaper fare.

Having spoke to Qantas I was told that the BA agent was "just being difficult" and that "she obviously wasn't clued in with internal procedures". He said it should cost approx $80AUD and could only be booked with BA. He said that he contacted BA through their "oneworld desk" to inform them how it should be ticketed correctly and that I should call BA back to get it sorted.

I am not too hopeful.....