Wairarapa councils have significantly underestimated the cost of becoming a unitary authority, says Greater Wellington Regional Council chairwoman Fran Wilde.
Councils in the Wellington region are considering options for the future governance of the region, and Wairarapa councils have agreed on a preferred option of a unitary authority.
Leaders disputed the amount subsidised by Greater Wellington this week when they argued Wairarapa can afford to become a unitary authority.
Figures provided to then-Carterton Mayor Gary McPhee in 2008 estimated the subsidy to be about $4.5 million, but figures provided in a report commissioned by the three Wairarapa district councils estimated this figure to be $11.2 million, and the mayors questioned why the figure was so high.
Ms Wilde said the report has a host of inaccuracies and the spend could not easily be reduced.
"The report paints a picture of regional council services that are either over-priced, unnecessary, unnecessarily comprehensive or easily abolished," she said.
"That could not be further from the truth. Our figures have been independently reviewed by PriceWaterhouseCoopers, and are a reasonable and conservative portrayal of the facts."
Ms Wilde said Wairarapa people have the right to decide their own future but it was critical they had "absolutely full and transparent facts" about the cost of the change.
She said there was an $11.2 million shortfall in what was collected in rates in Wairarapa and what was spent.
"A difference of that magnitude will confront any unitary authority established in Wairarapa, and it will not go away, no matter how hard you play with the figures as this report has attempted to do."
Ms Wilde said the $4.5 million figure did not include expenditure on public transport, and additional spending has come about with things such as possum control.
She also disputed Wairarapa's estimated annual dividend of $750,000 from CentrePort in the report to being about $400,000 based on population.
She said a unitary authority would also affect the Wairarapa Water Use Project which has $3 million budgeted by Greater Wellington in the next three years.
"I completely understand the sentiment of some who claim that their concerns might be drowned out by voices closer to Wellington as a result of re-organisation, and that's why I feel a two-tier structure for the region strikes the right balance between regional and local needs."