I too am currently in the UK and 24 hours ago was on the NZ website placing dummy bookings to determine various fare class availability and status earning and today this ability as you say to access the NZ site has disappeared.
I also use the NZ website to book cheap fares for when I will be in NZ - grab a seat etc
Have just spent the last 30 mins trying to find away around this and the only way was finding a NZ issued email offering NZ deals for NZ residents - clicking on the link enabled me to access NZ fares in $NZ
If you PM me I can forward you the email so you can gain access to the NZ fares and website thru this means
Not sure what is going on here or what they are playing at - tried accessing other countries and the gateway web address took me to the USA and Japan sites no problems