Steven Joyce is continuing to back his controversial claim there's a $11.7 billion hole in Labour's budget.
Now he says he might have been "too conservative".
"It really depends on Grant Robertson's attitude to expenditure," he told The AM Show on Thursday morning.
"Up until now, you have to say he's not acting like a traditional Finance Minister and the Government's not acting like a Government that's actually going to control costs. They might do, but virtually every day they have a new thing they want to spend money on."
Mr Joyce's insistence Labour was missing $11.7 billion to deliver its election promises was one of the election campaign's most divisive claims. Economists rounded on the then-Finance Minister, saying Labour's numbers added up just fine.
BERL executive director Ganesh Nana, said the hole was "a fiction arising from a disagreement over definitions". Sam Warburton of the pro-business New Zealand Initiative said National made a mistake. Even the Taxpayers' Union, made up of some of Labour's strongest opponents, said National's criticisms were only "partially correct" and if there was a hole, it wasn't $11.7 billion.
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Mr Joyce said Labour is announcing new spending every day, citing new funding for anti-HIV medication, hospice care and increased student allowances.
"Unless they rein it in… they're going to end up with quite a head of steam on, which taxpayers are going to have to pay for… Sadly I think we'll get to the $11 billion over time."
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While National borrowed heavily in its first twoterms in the wake of the global financial crisis and the Christchurch earthquakes, driving debt as a percentage of GDP up from 5.4 to 25.5 percent, there was no longer any need to do so.
"Why do we need to borrow more money at this stage of the economic cycle? … It's not like we've got a Christchurch earthquake to pay for."
Betwen 2014 and 2016, under then-Finance Minister Bill English, debt as a percentage of GDP fell to 24.6 percent.
The previous Labour-led Government delivered nine consecutive Budget surpluses under Finance Minister Michael Cullen. Mr Joyce said Mr Robertson should be more like the "grumpy" Mr Cullen and tell other Cabinet ministers to rein in their spending promises.