Marketplace
Malaysia Airlines is always a solid deal, and despite the inevitable jokes in the comments below, they're reliable, great service, and on time, in my experience.
Dates include Sep, Oct, and Feb-May for under or around a grand.
Airline: Malaysia
From: MEL from $991/PER from $945
To: London, UK
Alliance: OneWorld
Examples from Melbourne:
https://flightscout.co/au/cheap-flights/melbourne-australia-…
Examples from Perth:
https://flightscout.co/au/cheap-flights/perth-australia-to-l…
I also regularly choose Malaysian Airlines - good value, reasonable partner with Qantas FF (https://www.qantas.com/nz/en/frequent-flyer/earning-points/f…), friendly and courteous staff with real grace despite everything they must have been through with the trauma of those two lost flights, and flights generally not full booked. Happy to support them.