National would have enough support to govern alone if an election were held today, a Herald-DigiPoll survey shows.

In the last political poll for 2010, National has the support of 52.4 per cent of decided voters while Labour has 37.2 per cent.

The Greens are the only other party above the 5 per cent MMP threshold, on 5.3 per cent.

National's rating is down from the last DigiPoll survey of 56 per cent in February, and Labour's is up from 34 per cent.

Polling finished at the start of Christmas week. The majority party vote support for National reflects the trend of three other political polls in December and might suggest that Prime Minister John Key is well placed to lead National to govern for a second term at the next election, likely to be in November next year.

But the Herald-DigiPoll survey shows a narrower margin between the two big parties, 15.2 percentage points, than some other polls.

And no party since the first MMP election in 1996 has managed to get an outright majority of seats, even after discounting the votes of parties that fell short of the 5 per cent threshold, such as New Zealand First, which polled 4.07 per cent last election and got no MPs in Parliament.

In the December poll, New Zealand First is on 2.5 per cent, the Maori Party is on 1.2 per cent, Act is on 0.9 per cent, and the Kiwi Party, which has no MPs, is on 0.2 per cent.

Asked if the Government was moving in the right direction, 56.5 per cent said "Yes", 32.1 per cent said "No", and 11.5 per cent did not know.

Those results vary a little from February when 59 per cent said it was heading in the right direction, 28 per cent disagreed, and 13 per cent did not know.

Mr Key is overwhelmingly preferred as Prime Minister with 53.1 per cent (58 per cent in February) compared with Labour leader Phil Goff on 7.7 per cent (6.8 per cent), just ahead of former Labour leader and head of the United Nations Development Programme Helen Clark on 5.6 per cent.

New Zealand First leader Winston Peters, outside of Parliament, is on 3.3 per cent.

Deputy Prime Minister Bill English rated zero support.

But the preferred PM in this poll includes undecideds, and 24.6 per cent of respondents gave no person as preferred Prime Minister - not knowing who they liked, wanting no one or refusing to answer.

The 3 News poll, the One News-Colmar Brunton poll and the Roy Morgan poll all published this month had National polling above 50 per cent - 3 News on 55.5 per cent with Labour 24.3 points behind on 31.2, One News on 55 per cent with Labour 22 points behind on 33, and Roy Morgan on 53.5 per cent with Labour 18.5 points behind on 35 per cent.

At the last election, National won 44.93 per cent of the vote and formed a minority Government with Act, United Future and the Maori Party.

Labour was 10.94 points behind with 33.99 per cent of the votes.