The Maori Party and UnitedFuture would face a choice of switching sides to back Labour or forcing a new election on the numbers, according to a new Fairfax Media-Ipsos political poll.
OPINION: The poll effectively delivers a dead heat, with the governing parties and the opposition bloc each set to win 61 seats if the minor parties hold the electorates they won in 2011.
With ACT on the Right and Mana on the Left unlikely to switch camps, the heat would go on the Maori Party and UnitedFuture.
If no clear winner emerged in 2014, the prime minister's speech to Parliament would spark a vote of confidence, which the carry-over Key Government would need to win to stay in power.
If the deadlock was not broken, a new election would result.
The knife-edge result in today's poll shows how vulnerable National is when its support falls into the mid-40s, mainly because it lacks significant minor party allies, even though at 44.9 per cent it is well ahead of Labour on 36.3 per cent.
A bright spot in the data for National may be that, by a factor of two to one, undecided voters are leaning towards it over Labour. However, pollsters Ipsos suggested that could be because those voters might have recently left National and are yet to find a new home.
A big unknown is still NZ First, which at 2.8 per cent fell well short of the 5 per cent threshold for list seats under MMP.
If leader Winston Peters lifts its support during the 2014 campaign, a bloc of six or more seats could make him the kingmaker.
However, close co-operation with Labour in the manufacturing inquiry is building a united opposition on core economic policy that makes his support for a Centre-Left government more likely.
Today's poll is in line with the latest Roy Morgan survey, which put Labour-Greens in the box seat.
But last week's One News poll showed a much stronger result for National, with 49 per cent backing.
Today's poll shows a swing of 3 percentage points away from the National-led Government.
But it also highlighted how electorate seat distribution may be critical, including how many so-called overhang seats are created.
That occurs when a party wins more electorates than the seats it is allocated from its share of the party vote. When that happens the size of the House is increased above 120 to account for the extra seats.
Note: Ipsos has for the first time adjusted the method of calculating voting intention by now excluding those who do not intend to vote. This is consistent with new guidelines on political polls from the Association of Market Research Organisations and their European equivalent. The change has resulted in a minor adjustment of some figures of no greater than 0.5 percentage points.
- Fairfax Media