While you are of course correct that LHR is the only European destination served by NZ metal, I think what virtualtroy means is the best country from which to start the journey. Although this will involve either a connection to LHR (or, in the case of Germany, a codeshare LH flight to an NZ gateway) but this still usually works out cheaper, mostly because the UK market (like the US) is notoriously expensive to buy business class fares out of. I assume this is because it is such a centre of wealth and big business that the market will bear higher prices. One of the reasons airlines fall over themselves to get slots at Heathrow!

Having said all that, there have been some quite good discounted business class deals out of the UK recently - just over GBP2,000 IIRC. Zaco might know more. Have you tried the AirNZ Europe site?