The National Government must show voters exactly how much dividend revenue will be lost under its asset sale plan after last week saying Labour had got those figures wrong, Opposition finance spokesman David Cunliffe says.

The Greens also say the Government is not telling the whole story on the returns taxpayers will lose under the plan.

Accused by National of having a $17 billion "hole" in their figures, Labour on Friday provided detailed numbers ahead of an election where it is promising ambitious economic reforms including a capital gains tax.

The figures showed that to offset the lower tax take over the first four years of Labour's plan it is counting on $868 million in dividends that would be lost under National's mixed ownership model or partial asset sales.

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However, National and the Treasury said Labour had used the wrong data, and Finance Minister Bill English said the dividend income had been overstated by $400 million.

Labour's error in using forecast figures that included Kiwibank's interest revenue was "symptomatic of the problems" across Labour's entire costings, Associate Finance Minister Steven Joyce told TV3's The Nation on Saturday.

Yesterday, Mr Joyce reduced his estimate of the extra borrowing Labour would require over four years from $17 billion to $15.6 billion. Labour says its extra borrowing would be $4 billion, not including the $6.8 billion it would borrow to resume NZ Super Fund contributions.

Mr Cunliffe yesterday said Labour had used "the best publicly available information" and it was up to National to provide evidence they had got it wrong.

"The Government's reaction has effectively conceded that they have failed to disclose the loss of dividends. It is for them now to disclose based on more detailed data that they have internally available exactly how big the dividend loss is."

Labour's figures suggest it expects $845 million from the relevant companies in the 2012/13 year rising to more than $1 billion in the next and subsequent years.

Mr Joyce says those companies, of which his Government will sell as much as 49 per cent, paid combined dividends to the Crown of about $350 million to $360 million a year.

Data from the Treasury's Crown Ownership Monitoring Unit (Comu) show the annual average combined dividend over the past four years has been $580 million. That figure has been swelled by large capital returns, particularly from Meridian when it sold dams in Australia and the Tekapo A and B dams last year. Even before those events it was paying dividends of about $300 million a year, Comu said.

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Adding in the increasing value of the companies' assets to their dividend streams, the companies earmarked for partial sale have posted total returns to the Crown of up to 28 per cent for Meridian and Air NZ, with the lowest being Solid Energy with 7.5 per cent.

Yesterday, Greens co-leader Russel Norman, whose party wants to retain the energy SOEs and incentivise them to work with private sector partners to develop renewable energy technology exports, said the total return from the companies was the figure the public needed to look at.

Mr English's office last night said the $400 million shortfall in Labour's numbers was calculated against forecast dividend returns that did not include any potential capital returns and it was the Treasury's decision not to include those forecasts in the Pre Election Economic and Fiscal Update.