I was there in January, and I've never seen a MTB scene like that (granted I've never biked in the UK either). Seems there where biking centers all over the place and trails where amazing.
http://www.bikepark.co.nz/trailmap.html
Woodhill was close to Auckland, less then an hour by car. It cost a few dollars to enter, but not very much. The trails had great flow and luckily there was an emergency center fairly close (don't go riding very fast on your first day after flying there from Europe).
http://www.riderotorua.com/maps.php
Roturua had amazing trails, anything from world cup DH runs to flowing trails. They are all free, if you want a shuttle to the top it will cost a few coins.
I did'nt have the chance to go to any other centers, but there are plenty of them. There is also a pretty active scene on the south island (did not visit).
I've traveled to a lot of countries and NZ I can't think of many I'd rather live at then NZ. There did seem to be a lot of road biking in Auckland, but the mountainbiking scene is far from dead. I don't think there where a lot of trails right next to the town though. We went to most places by car, don't think there is very good public transportation.