Experience World´s longest non-stop flight which is about to commence on 3rd of December 2016 (postponed to 1st of February 2017) on route Doha - Auckland (17h 30min) and fly on board of Qatar Airways, airline of the year 2015! Round trip tickets from UK to New Zealand are now available already for £571.(€687). Look for routing Manchester or London to Auckland. 
If interested in this solution with Qatar Airways to New Zealand you may find limited travel options when departing from UK from 1st of February till end of May 2017. Max stay 3 months. Booking has to be done till 1st of July 2016. Please refer to below booking and travel date samples.
Booking samples
London - New Zealand from £604 (or with Air China from £573)
Travel date samples
6. - 26.2.2017
12.2. - 6.3.
5. - 25.3.
23.4. - 6.5.
7. - 27.5.
If you consider to book these cheap return flights to Auckland you may compare connection flights from your hometown using service of Skyscanner. This tool helps you quickly find which low-cost airline is connecting from your city. Some of the flights may require long layover in Doha. This carrier is offering free hotel in transit Further details here. Need an accommodation in New Zealand you may use Booking.com or consider following promo codes offred by Hotels.com, Hotelopia or Venere.
Booking sample of Experience World´s longest non-stop flight to New Zealand from £571 here. In this case you would fly from Manchester to Auckland on 19th of February 2016. Your return flight from New Zealand back to UK would be on 12th of March 2017.
