I once flew with United from Amsterdam to Sydney via LAX
for 800 euro including taxes, specials they sometimes have off season (febr-may) although now the taxes will be a bit higher.
With the detour over the US, this comes to about 29.000 miles for the equivalent of 550 GBP, which is about the same price level as your trip.
In the Europe-Australia market, the last few years prices start at this level and might be the ones coming close. Also the NYC-California market starts at about $75 one way and with the cheap dollar two of these sectors (about 3000 miles?) can make up a cheaper trip. Of course Ryanair, Jetsgo and other LCCs sometimes offer almost free tickets but the catch is it will be hard to make a multi itinerary trip with only these fares.