I expect you’ll be fine.

NZ passport holding arriving passengers can use e-gates at Auckland, so queues for Immigration are usually pretty short - I’d be surprised if you wait more than 5-10 minutes (unless you get stuck in a queue of other non-NZ passport holders), and it could easily be less, especially if you’re one of the first off the flight. I suggest you check if UK passport holders can use the e-gates - I doubt it, but don’t know.

There can be longer delays for Customs after you collect your bag, as everyone goes through there (even with different lines). Customs can take 10-20 minutes or even more if things are busy.

Once you exit to landside you need to turn right and walk about 100m along the terminal to the international departures check in area (which is on the same level as you’ll exit after Customs).

As you’ll know, check in is usually 2 hours before the flight but it will be open earlier. If your flight is on time you could easily get from plane to check in within 30 minutes on a good day, and 60 minutes on a bad day.

After check in you’ll need to go up one level, do another security check and Immigration departure. That normally takes no more than 10-15 minutes, so you’ll have plenty of time for the Koru Lounge (if you’ve got access to it) or the airside shops.