I apologise if anyone is getting bored of these flight deals, but these are the cheapest flights I've ever seen!
If you go to Expedia's Australian site you can take advantage of the exchange rate. Currently, they are offering return flights from Heathrow to Auckland for under £400!
9th May - 23rd May: $846 AUS - £397
16th May - 23rd May: $846 AUS - £397
23rd May - 6th June: $846 AUS - £397
If you don't fancy going all the way to New Zealand, then it'll cost you more to get off the plane early (?!?). Flights to Sydney are $902 AUS ... or about £422!
All these flights are with British Airways, though there are other airlines for a few pounds more. The best deals seem to start in April/May. Please check your bank before booking as you will be charged in Australian dollars ... make sure you know what the conversion charge is.
EDIT: Not sure why the link takes you to an Expedia 'Price Promise' page (it does for me) ... I assume this is something to do with the HUKD ...