United Future leader Peter Dunne is quitting politics at the election, in a shock announcement made today.

Dunne cited recent polling for his decision to quit politics after more than three decades.

In the latest twist to a chaotic election, Dunne is the third leader in just three weeks to resign, following Labour's Andrew Little and the Greens' Metiria Turei.

"The current political environment is extremely volatile and unpredictable," the Ohariu MP said in a statement.

"However, I have concluded, based on recent polling, and other soundings I have been taking over the last few weeks, that, the volatility and uncertainty notwithstanding, there is now a mood amongst Ohariu voters for a change of MP, which is unlikely to alter."

Dunne has been an MP for 33 years. He was facing a serious challenge in Ohariu from Labour's Greg O'Connor, the former Police Association president.

O'Connor paid tribute to Dunne, saying he had been a "very, very effective local MP" who had been loyal to Ohariu.

"Yes, it's a surprise," O'Connor told the Herald.

"But this is an election like no other."

O'Connor said Dunne's resignation did not change his campaign.

"I've still got a lot of work to do. It certainly doesn't mean that the seat becomes any easier."

Dunne said he had decided it was time to stand aside: "After much consideration and discussion with those closest to me, I am announcing today that I will not be putting forward my nomination for election to the next Parliament. I do so with considerable reluctance, but I have always understood that holding public office is a temporary privilege granted by the people, and can never be taken for granted.

"I have thoroughly enjoyed serving the Ohariu electorate in its various forms since 1984. I thank my constituents, my supporters, my party, and all those staff members who have worked so loyally and professionally alongside me over the years, but above all, I pay huge thanks to my wife Jennifer, my sons, James and Alastair, raised in the heat of politics, and my entire family for their loyal support, patience and encouragement for so long. 

"I am especially proud to have worked alongside successive National and Labour-led governments in the collaborative environment of MMP, and to have had the privilege of serving as first an Under-Secretary and then a Minister under seven different Prime Ministers for just on fifteen years. I am very proud of the many changes I have been able to make in my portfolios over the years to make New Zealand a better place in which to live and raise a family."

Prime Minister Bill English had explicitly told National voters to give their candidate vote to Dunne rather than National's candidate Brett Hudson.

Dunne said he made his decision with "considerable reluctance".

"But I have always understood that holding public office is a temporary privilege granted by the people, and can never be taken for granted."

Dunne said Ohariu had been a "very large part of my life" and he has raised his family there. Representing the electorate had been "an absolute delight".

"But good things cannot last forever. Now it is time for me to put all that behind me, take the election hoardings down, say goodbye to Parliament without bitterness or regret, and get on with life."

In a recent profile for the Herald, he said at age 63 he had occasionally considered retirement, but still enjoys "the buzz of involvement" and in particular the chance to help people.

"I look around and think, 'if I wasn't doing this, what could I do to replace that?' "And I haven't found an answer yet."