Prime Minister John Key’s defeat in the flag referendum has not dented his party’s support, a new poll shows.

The Labour Party, on the other hand, has fallen below the crucial 30 percent threshold for the first time since the election, and leader Andrew Little is less popular then New Zealand First's Winston Peters in the preferred Prime Minister stakes, in the latest TVNZ Colmar-Brunton poll.

It showed that National had risen three points to 50 per cent - its highest result in the poll in a year.

If an election was held tomorrow, National would be able to govern alone.

Labour fell four points to 28 percent. The drop below the 30 percent threshold will be a significant mental setback for Labour, especially because it has made major policy announcements this year.

Labour unveiled a multi-billion dollar plan to give every New Zealander three years of free tertiary education in January. It also revealed some of its high-level Future of Work Commission findings.

Little said the result was “obviously disappointing” and reflected a “bad couple of weeks” in March.

“I think it’s a question of us knuckling down, understanding the need for a clarity of message, and sticking to the things that are important to New Zealanders,” he told the Herald.

In late March, Little was mocked in Parliament after appearing to lay the blame for a migrant boom on ethnic chefs. Labour’s consideration of a universal basic income in New Zealand was also questioned because of its potential cost.

Little and most of his caucus opposed a change of flag in the referendum last month, and the party made a strong stand against New Zealand signing the TPP – a stance which caused some pro-free trade MPs to break ranks.

The Labour leader fell slightly in the preferred Prime Minister poll, dropping two points – within the margin of error – to seven percent.

That meant he was overtaken by Peters, who moved up one point to 10 percent.

National’s positive result came despite Key’s public advocacy for a change to a silver fern flag, which was soundly defeated in a referendum last month.

Key’s preferred Prime Minister ranking was barely moved, falling one point to 39 percent.

This year, the Government has been promoting the Trans Pacific Partnership deal around the country in a series of roadshows.

The April 6 cut-off date for the poll meant it was unlikely to have taken into account any possible fallout from the Panama Papers scandal, which shone a light on New Zealand’s tax-free foreign trusts.

Despite leading a strong campaign against a flag change, New Zealand First’s support was nearly unmoved, falling one point to nine percent.

The Green Party, which announced a policy to make Kiwibank more competitive, rose two points to 10 percent.