This airfare involves 2 bookings - first from Perth or Melbourne to Kuala Lumpur and then from KL on to London. The stopover in KL can be a few days each side (or just a few hours if you are feeling adventurous). Flights are in September through to December and there are lots to choose from.
Here are some example dates.
Departing Melbourne 3/Sep arriving in Kuala Lumpur on 4/Sep.
Departing Kuala Lumpur 6/Sep for London.
Departing London 25/Sep arriving in Kuala Lumpur on 26/Sep.
Departing Kuala Lumpur for Melbourne on 27/Sep.
Melbourne to Kuala Lumpur Flights $351 Jetstar
Kuala Lumpur to London Flights $636 Royal Jordanian
Total $987
Departing Perth 4/Sep arriving in Kuala Lumpur on 4/Sep.
Departing Kuala Lumpur 6/Sep for London.
Departing London 25/Sep arriving in Kuala Lumpur on 26/Sep.
Departing Kuala Lumpur for Perth on 27/Sep.
Perth to Kuala Lumpur Flights $199 Jetstar/AirAsia
Kuala Lumpur to London Flights $636 Royal Jordanian
Total $835
Payment using POLi and Visa Credit Card. Slightly more for other payment methods.
There are lots more dates available, just find the dates from Kuala Lumpur to London that work for you & then work out the connecting flights.
Kuala Lumpur to London Flights
Here is Perth to London for $1098 in one booking:
http://iwantthatflight.com.au/flight.ashx?oc=PER&dc=LON&dd=22/Apr/2016&rd=15/May/2016
And from Melbourne for $1183 on Royal Brunei in one booking.
Melbourne to London Flights