Thanks for the reply but I'm still not convinced
If I price the sectors out on www.itasoftware.com;then each transit gets charged GBP21.50 which is the UK Passenger Service Charge. GBP63.50 is about AUD114 . If ITA is correct then the Oneworld booking engine is incorrectly charging the UK Air Passenger Duty on every transit. Is there an exemption for less than 24hr transit or has ITA got it wrong?