Judith Collins dismisses '$4 billion gap' as 'entirely inconsequential', says Jacinda Ardern should apologise

Judith Collins is dismissing the '$4 billion hole' found in its fiscal and economic plan as "entirely inconsequential" - and says Jacinda Ardern should be the one who apologises.

Earlier on Sunday Labour's finance spokesperson Grant Robertson revealed National had used May's Budget figures instead of last week's Pre-Election Economic and Fiscal Update (PREFU) numbers - a difference of $4.3 billion.

Robertson said the error begs the question of whether there are more mistakes in National's plan.

"Not only is National's proposal irresponsible when New Zealand needs stability and certainty, they are showing they lack the experience to run the economy. There is no John Key or Bill English there anymore. No one who knows how to run a Budget would have made a basic mistake like this."

But speaking after National's campaign launch on Sunday, Collins says the mistake "means very little".

"It's actually over 10 years," she explains.

"It's the difference between a 35 percent debt-to-GDP ratio and a 36 percent. That's nothing compared to Labour's 48 percent. It's actually only a matter of projections."

National's finance spokesperson Paul Goldsmith said he's apologised to Collins for the error, but Collins believes there's someone else who needs to apologise - Labour leader Jacinda Ardern.

"Jacinda Ardern should apologise for promising New Zealanders that $2 billion would kickstart the KiwiBuild programme, that 16,000 houses would now be built and now there's 500," she says.

"When we talk about this it's best to remember, you know, 100,000 houses promised for Kiwibuild, child poverty, children being told that material hardship for children would go down significantly - it's gone up for 4000 children in three years. You just think about the state house waiting list.

"I think people understand that an error was made and that it was owned up to and actually I've got no problem with that. The fact is if everybody went through life thinking that they could never ever make an error, actually no one would get out of bed in the morning."

Collins adds Goldsmith is "feeling very bad on it".

"I didn't have to say anything. As you can imagine… when I've got really high performing people and there's a little error, you know what, they're feeling bad themselves and so Goldy didn't need me to tell him off."