The Green Party has criticised the $65 million cost of selling shares in Mighty River Power to the public.

Greens co-leader Russell Norman said new figures from Treasury revealed the total $65.8 million cost, equivalent to 3.9 per cent of the sale proceeds - more than the 2 per cent figure previously estimated.

That amount was made up of $28 million in Treasury costs, $12.8 million spent by Mighty River Power, and $25 million in bonus shares.

"The Prime Minister wasted over $65 million of public money on selling Mighty River," Dr Norman said. "Only 2 per cent of the population bought shares; the rest of us had to pay."


"All up, National's asset sales programme has cost $115 million and the bill keeps climbing every day. That money should have been spent on important public services, not wasted on brokers' fees, lawyers, and ad men."

In parliament on July 24, in response to questions from Dr Norman, Mr Key said the current best estimates of the total cost were about 2 per cent of the proceeds.

He also said the government was taking advice on how the bonus share scheme would be paid for.