Also BA has been pricing non-UK origin premium fares much lower than starting at LHR, you might check AMS-LHR-Oz to compare prices, it may be cheaper even when including the cost of AMS-LHR-AMS flight (this also reduces or eliminates the UK APD of GBP 90 depending on how you position). QF does often offer cheap FRA-Oz premium fares, so that might be cheaper than the BA price ex-LHR and would get you the QF squiggles.