Yes, World cruises. You can do a NZ/UK sector on P&O, Cunard, Saga et.
The world cruises just set off from Southampton this last week so you would be looking around March time for them to reach NZ for you to pick them up. You have a once a year window for this - so if not this March then you wait till 09.
P&O World Cruises reach New Zealand in February each year. This year Aurora arrives and leaves Auckland on 11 February for the voyage back to Southampton via Suez Canal. I'm booked on it! I think you will find that the Cunard Queens Victoria And Mary usually reach New Zealand in February.