The referendum on John Key
Just as the 1997 referendum on superannuation turned into a referendum on its sponsor, Winston Peters, so the referendum on the NZ flag became a referendum on John Key. The evidence for this is clear from the electorate results of the flag referendum. The correlation coefficient between each electorate's votes for the silver fern flag and the percentage of party votes for National in the 2014 election is a very healthy 0.95.
The weird aspect of this is that the electorates most in favour of changing to the silver fern flag were the most conservative ones, like Clutha-Southland and Tamaki.
But the really bad news for National is that the vote nation-wide went against the Prime Minister's desired option: only 43.2% in favour, compared with their overall party vote in 2014 of 47%. Keep in mind that, in the general election, voters had a wider range of choices, while in the referendum there were only two.
The referendum indicates that Key (at least temporarily) has lost the support of about 4% of voters, or maybe more, enough to cause an upset at a general election. For the first time perhaps, many who have been consistent Key supporters have ticked a box that effectively said 'no' to him.
National have enough time between the flag referendum and the next general election in 2017 to recoup that loss. After all, it was only about a flag, and political memories can be very short sometimes. But they have work to do if they are to prevent this from becoming an electoral 'tipping point'. Note that only 39% were in favour of the silver fern in Northland, the same electorate that voted out a National candidate in early 2015 (in favour of Winston Peters, who then opposed changing the flag) and that used to be a safe National seat.
Take-home message for politicians from the flag vote is: 'Don't start a referendum unless you really have to, or are really confident of your support.'