Council officials have become embroiled in a war of words with a leading academic over whether she has fully shared her research which she argues makes a strong case not to build the controversial Western Link road.
Dr Charlotte Packman, an ecologist, has carried out her own studies of the proposed route of the 3.9-mile road, linking the A47 and NDR, which she says show far more endangered bats living in the area than Norfolk County Council's own research.
She claims that to build the route would have a "catastrophic impact" on a nationally important population of barbastelle bats and that the scheme should be scrapped. She claims the council has ignored her research.
But County Hall officials have accused the academic, who is the director of University of East Anglia-based Wild Wings Ecology, of not fully sharing her data, despite their repeated requests.
She has hit back, saying they have had "more than adequate information".
Norfolk County Council has already altered the route of the proposed £274m Western Link, after its own surveys showed the presence of barbastelle bats in woodland.
But Dr Packman, who has been working with Norfolk Wildlife Trust, said the creatures were far more widespread than the council had accepted.
"We have recorded many more barbastelle roost trees, more extensive use of the landscape and much higher colony numbers, all of which strongly indicate this is the largest population in the country and that this area is undoubtedly of national importance for this very rare and special species.
"It is very clear, given the bat use of this area and its considerable importance, their proposed mitigation will not be sufficient to safeguard the population."
In 2021 the council announced its surveys had identified roosting bats and tweaked the road's route.
Dr Packman said: "Had they carried out adequate surveys, critically, in advance of selecting the route, as they should have done if guidelines and best practice had been followed, they would have located the colony and as a result, one would hope, would not have decided to put the road through there."
A spokeswoman said: "Some information has been shared with us by Dr Packman, however, crucially, the bat survey data that has informed this information has not.
"We have requested this data on a number of occasions but this has not been shared with us to date.
"So our position on this remains the same as it has been in the past - it isn’t possible for us to comment on the conclusions that have been drawn about any findings of these surveys without seeing the data behind them and we remain keen to see any information that could be relevant to the development of the project’s proposals."
The spokeswoman added it was "entirely normal" to carry out further surveys once a single route had been chosen and to develop the route based on those findings.
But Dr Packman said she had met council officers and shared data and information, including a map showing barbastelle home range areas, flyways and roosts, plus data about colony counts, acoustic survey data and details of collection methods.
She said: "The council has received more than adequate information from us for them to be able to understand our methods and results, to see that those are valid and that they have an insurmountable ecological issue.
"There is no reasonable justification for them to continue to ignore our evidence.