QF and BA pax travelling on same flight number services from Europe to Australia will have to pay the highest air passenger duty, as the APD is calculated based on the final destination of the plane from the UK.
I don't think that's quite right. I thought it was from the first port outside of Europe? Thus EK, Qatari, etc still have the competitive advantage by hubbing only 5-6 hours from Europe as opposed to Cathay, Thai, SQ, QF, JAL, etc who are all 12-14 hours from Europe but at least it's not based upon Sydney for QF.