Prime Minister Helen Clark's previously undisputed position as the country's preferred leader is under threat in the latest One News Colmar Brunton poll.

Not only does the new poll show National leader Don Brash now virtually neck and neck with the Prime Minister, but his party is continuing to hold its lead.

Clark is still on top in the preferred prime minister stakes, but she has slipped three points to 32% in the new poll.

Brash has climbed two points to leave him sitting on 31%, just one percentage point below Clark.

The only other contender in the leader poll was New Zealand First's Winston Peters who held steady on 7%.

The poll's party results did not provide any happier news for Labour and any question that they had clawed back ground from National is dismissed.

The past month has been yet another tough one for the government as the foreshore rebellion by Labour MPs rolled on.

The seabed vote was saved by a controversial deal with New Zealand First leader Winston Peters that put him back on the front pages and angered Labour's traditional supporter, United Future leader Peter Dunne.

Meanwhile, the 'Hurricane Brash' documentary does not seem to have damaged National's ratings.

National has dropped one point from the last Colmar Brunton poll to a 48% voter share, while Labour has dropped two points to 37%.

The new poll puts the Green Party back in the frame by giving them three points to reach the magic 5% this month. Also up 1 point to the 5% threshold is New Zealand First.

Under MMP, parties without an electorate MP must get 5% of the party vote to get into parliament.

The news is not so good for Act and United Future, which were both steady on 2% support.

However, the position is more secure for United Future because Dunne will almost certainly hold his electorate seat and keep the party in parliament.

The poll questioned 1000 voters and has a margin of error of 3.2%.