Labour Party leader Andrew Little said the Government had not been straightforward with the public about the SkyCity deal.

"I think it's disappointing that it's taken now for the truth to come out. The Government should have been straight-up with New Zealand well before now," Mr Little said.

Green Party co-leader Metiria Turei said the latest revelations proved Economic Development Minister, Steven Joyce was on SkyCity's side.

Steven Joyce Photo: RNZ / Alexander Robertson

"He is not batting for New Zealand when it comes to the SkyCity deal ... He and John Key and the Government knew about the cost blow-outs just after the legislation was passed and they kept that hidden from the country all through the election campaign," she said.

But Steven Joyce said the preliminary costings were not considered unusual at that stage.

"You can't get too excited about an early estimate which says it's a bit over but certainly by the time the preliminary design came out in October the extra cost they identified was of a magnitude that we felt should be in the public domain."

Mr Joyce said it was outrageous to suggest the Government misled the public over the costings.