First of all, it’s worth noting that a return business class fare from AUS to London will almost always cost more than $6-8k if you want to go with Qantas, BA or Singapore Airlines. You’d normally be looking at close to $10k per person with those airlines (although sometimes you can get specials).
But the good news is, my favourite airline for business class to Europe is Etihad, and a business class return with them normally costs around $7-8k. The reasons I love Etihad are:
(i) Guaranteed completely lie flat beds on all flights, with every seat in Business having direct access to an aisle. You also have the option of individual (and this very private) seats, or 2 seats beside eachother (great for couples).
(ii) They have a “dine on demand” service, which means you can eat anything on the menu at any time during the flight. I’m not aware of any other airline that provides this option in Business. This is a godsend if you want to sleep at the time when they would otherwise be serving the main meal. I hate having to choose between tiredness or hunger!
(iii) Generally great food and service, and no issues with free flowing alcohol. Plus a nice bonus of free chauffeur transfers to/from the airport.
The only downside travelling with Etihad from Brisbane is that you need to connect twice (in Singapore and Abu Dhabi), but you can fly direct from SYD or MEL to Abu Dhabi if you see that as a problem.
Singapore Airlines business is also awesome though, if you don’t mind paying a bit more, and if you are not bothered about the dine on demand service or chauffeur.
Another cheaper, but still pretty good, option is Malaysia Airlines. Definitely not in the same league as Etihad or Singapore, but you can often get return Business fares to Europe with them for less than $6k. If you do that though, just be careful to avoid the code shares with KLM (as I believe it’s pretty bad!). I’ve also gone with Air France, which was pretty good and can often be quite cheap (and you go with Qantas as far as Singapore or Hong Kong), but if you specifically want to go to London a downside is that you’d have another connection after arriving in Paris.