Prime Minister John Key has changed his position on the sale of Kiwibank and now says there will be no sale or part sale while he is Prime Minister.

Staking his leadership on the pledge puts it in the same league as his promise on superannuation, where he said he would resign as Prime Minister if he cut superannuation.

Last week the notion of a part sale of Kiwibank through a share float remained a possibility by National in a second term.

Now it is completely off the agenda.

Finance Minister Bill English had raised it at a post-Budget lunch in response to a question from the audience.

He restated National's position of there being no state asset sales this term and he singled out the possibility of a partial share float of Kiwibank in the future for small investors.

Mr Key also restated the policy last week at his post-cabinet press conference and talked about his preference for the Government to hold a majority shareholding if there were a float.

But earlier this week opposition party researchers had found quotes from Mr Key from the election campaign in which he said he would not sell Kiwibank. "I'm ruling out selling Kiwibank at any point in the future," he said on the TV3 leaders debate.

Both Mr Key and Mr English have said that statement was consistent with the position of the party reviewing its moratorium on asset sales before the next election.

However, answering questions in Auckland yesterday Mr Key was asked if he would rule out any sale of Kiwibank at any time in the future.

"Under my leadership, yes," he said.

A spokesman later said that also included part-sale.

Labour leader Phil Goff said through a spokesman: "National and John Key's constantly changing positions show they cannot be trusted to keep Kiwibank in Kiwi hands.

"This latest statement won't end the matter because New Zealanders won't be fooled.

"People know they really want to sell Kiwibank but won't say so because it is deeply unpopular."