slippers Auckland you will get plenty of job offers!!! Problem with Auckland is the high cost of housing, but I know plenty of people that live there on two wages comfortably..depends on what you expect in terms of lifestyle really, but then we are never going to be rich being social workers are we?
You really shouldn't have any problems getting work at all in the North Island. Lots of little gang hotspots all over the place i.e Hawkes Bay, Wairoa, Wanganui, Rotorua but you would probably be not working exclusively with gangs but working with families who are associated to gangs. One thing to keep in mind is that NZ is bicultural, so you will need to show a willingness to learn NZ history and the impact for NZers now (both Maori and Pakeha), and where you would fit in as (I presume)a white? English social worker.
Wellington is another place to look at. Would have lots of interesting work and you are in the policy hotspot if you ever wanted to move in that direction.
Instead of LA's they have one central govt/stat agency Child, Youth and Family CYFS. So no matter where you work, if you do statutory work it will always likely be with CYF. Just remember if you are in a small city it can be difficult to escape your clients, not like London where you can have relative anonymity!
The main difference I think is the perspective, in NZ the emphasis is on keeping the family together. It is not nearly as punitive as the UK, however, not sure if this is for the best as to our shame in NZ we have some of the highest rates of child abuse. But it is a very different way of working, can be frustrating but also good for children to stay within their families or nearby but have regular contact/interaction with their family.
I would hope you would find social work a bit more "pure" in NZ, less paperwork, less bureaucracy but I am sure child protection in South Auckland is up there with child protection teams in London in terms of caseload and stress levels.
Sorry OP, we keep going off your topic....but I am reading with interest all the updates from everyone!