National's Finance Minister Steven Joyce is sticking to his guns, claiming that a Labour Government would create an $11.7 billion fiscal hole despite this allegation being widely criticised since he made it two weeks ago.

Joyce faced off with Labour's finance spokesman Grant Robertson at this morning's Mood of the Boardroom debate, hosted by the Herald.

The two men vying to take control of the country's coffers after the September 23 election broadly reiterated the messages of their respective party leaders. Joyce continued Prime Minister Bill English's criticism of Labour's failure to clarify what its tax policy would be should it come to power.

Robertson rehashed Labour leader Jacinda Ardern's attack on the Government for failing to address the country's housing shortage until the "11th hour".

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Perhaps the liveliest moment of the debate came when moderator Shayne Currie quizzed Joyce about his controversial allegation that Labour had an $11.7b hole in its spending plans, something that has been dismissed by both Labour and numerous financial experts.

"Yes it does [exist]," Joyce said, drawing laughs from the crowd.

"I'm very very concerned about it. I genuinely am concerned about the level of debt that a Labour Government ..."

Robertson interjected, stating he had been forced to address "two weeks of you making things up".

"Steven you have actually embarrassed yourself again this morning," he said. "We have put out a fiscal plan that has been fully costed, independently audited and not one economist in the last two weeks has backed what you have just said right now.

"For me this is Trump-like, it's fake news and it is an attempt to distract from all of the issues and the problems that we've been discussing today. You're actually making a fool out of yourself."

Joyce countered that Labour's own numbers showed the country's debt after five years would be $11.5b higher than how the economy was currently tracking.

"To believe it wouldn't be any higher than that you'd have to believe firstly that a Labour Government would spend less than a National Government, you'd have to believe that Labour would deliver two $0 budgets ... and you'd have to believe that all these proposed taxes would have no impact on the New Zealand economy," Joyce said.

"If you believe all of that then I have a very good railway company to sell you."