More great prices via IWTF's home page. Fares are for payment with a debit card. A small additional fee applies if paying by CC.
Valid for travel Oct to Nov 2016. Some sample dates below. Safe travels :)
Melbourne to London - Heathrow return
Dep. 11/Oct Ret. 26/Oct $951
Dep. 14/Oct Ret. 05/Nov $951
Dep. 18/Oct Ret. 31/Oct $951
Dep. 21/Oct Ret. 31/Oct $951
Dep. 18/Oct Ret. 03/Nov $981
Dep. 25/Oct Ret. 10/Nov $981
Dep. 01/Nov Ret. 17/Nov $981
Sydney to London - Heathrow return
Dep. 11/Oct Ret. 26/Oct $997
Dep. 11/Oct Ret. 31/Oct $997
Dep. 14/Oct Ret. 31/Oct $997
Dep. 14/Oct Ret. 05/Nov $997
Dep. 16/Oct Ret. 31/Oct $997
Dep. 18/Oct Ret. 31/Oct $997
Dep. 21/Oct Ret. 31/Oct $997
Booking through Bestjet (Australian) so Flight Centre will beat by $1 and may let you pay with CC
Alternatively BYOJet (booked through skyscanner) is giving the first Sydney trip (And possibly others) for $996 if paying with Visa Debit.