christep

With an Australian passport, probably not. The argument for BN(O) when otherwise only holding an HKSAR is that if you find yourself needing consular assistance somewhere then you might prefer to be getting it from the British consulate than the Chinese one. But if you can get it from the Australian one then no problem I guess.

Having said that, your status as a BN(O) is not dependent on renewing your passport - it's a status that you have for life unless you renounce it, so at a pinch, if you are carrying an expired BN(O) passport to prove your status then you could probably get British consular assistance anyway.