QF typically only roster their UK crew 24hrs of less . Sometimes it’s less than 20hrs rostered in SIN.
AU/NZ crew tend to need higher rest requirements than the UK crew due to union agreements. Once a significant delay happens out of Heathrow , the impact on the crews rest can have implications for them operating the return sector.
There’s a reason there’s a UK base for cabin crew …cost cutting not just on wages but also on allowances /hotels and rest requirements (due to less slip time required by their contract )
Same as the NZ based crew -paid significantly less from AU based crews.