This is an Ancestry.com search which is free. Passenger lists into the UK 1878 - 1960. It does not appear to have captured all the incoming passengers for I know of two people who left for London in 1905 and they are not on the list. However, it is a good source of birth dates, if you are lucky enough to have travellers in the later time frame. You can choose New Zealand as a departure port but I guess some passengers would be listed via Australian ports as well. Perhaps that's where mine are.
Just sign into Ancestry.com with you free account no.