Following on from our previous post:

We have since had this reply from the Immigration New Zealand on-line help facility:

Thank you for taking advantage of our Online Help facility.
As long as you are permitted to stay in NZ till the date on the ticket either through the visa waiver arrangement or having previously applied for a visa. It is an outward ticket to a country which you have right of entry to. It does not need to be your home country.

Kind Regards,

Customer Service Officer
Department of Labour
I'm still quite glad that we've got return flights as there would be nothing worse than having issues about being let into the country, but it does seem that the option of a one-way flight to NZ with onward travel to Australia is still viable for UK passport holders entering on a tourist visa.