Large surcharge for departures from the UK ( with a few exceptions eg Inverness) .
Its a government levied fee and varies according to which class you are travelling and the distance your first sector travels . I think 2000 miles is the magic number .
It is more complicated than this - and it does not apply to arrivals only departures .
The cost can be substantial well over AUD 1100 for business seats plus all the other fees !
There are a few workarounds .
Air Passenger Duty - Wikipedia is a good reference but may not be totally up to date as some fee increases occurred this year.