"The report has not supported claims from the councils that a unitary authority is the best way to go. We also question their figures, which appear to be no more reliable than the ones they criticise.
"The report claims that there is no guarantee that the super-city option will retain Wairarapa subsidies or if the region will receive anything more than token consideration. However, there is no guarantee that a Wairarapa unitary authority will maintain current levels of environmental services, transport links or keep rates increases to a reasonable level."
Greater Wellington Regional Council chair Fran Wilde said the report comprised many inaccuracies.
"The authors of this report have taken a best-case scenario approach and have used the most optimistic assumptions for a Wairarapa unitary and the most pessimistic assumptions for a single council for the region," she said.
"Despite the fact that the allocation of cost is not an exact science, several of the assertions and assumptions made in this report are simply wrong. I am disappointed that such reputable companies have delivered what can only be described as an unbalanced study."
She said assessment of local democracy is vague and mostly opinion and other major concerns from GWRC include analysis around public transport, environmental and water issues and the impact of creating a Wairarapa unitary authority on the rest of the region.
Fran Wilde said a unitary council for Wairarapa would not be able to provide the level of resource, either financially or in terms of staff support and expertise, because this predominantly rests in Wellington.
"This report does not take into account the complexity of public transport, water and environmental issues, the size and scale of scientific monitoring, the amount of enforcement and compliance work, the investment in working on non-regulatory programmes, or the community's demand for information," she said.
In a statement, the working party refuted the claims.
"MartinJenkins repeatedly stated during their presentations to stakeholders in the Wairarapa, and in their independent report, that they have in fact been deliberately conservative in their approach to the financial viability question.
"Now that the Wairarapa Governance Review Working Party has had time to assess the MartinJenkins report, we have found that the assumptions are in line with what might be expected."