Campaigners who want to stop the £153m Western Link have accused County Hall of dismissing reports about the road's impact on a 'super colony' of barbastelle bats.
The Stop The Wensum Link campaign has sent a letter of complaint to Tom McCabe, Norfolk County Council's head of paid service, ahead of a key decision over the future of the mooted road on the edge of Norwich.
The controlling Conservative cabinet is due to meet next month to make a decision over awarding the contract to build the 3.9 mile road and to submit a business case to the government.
The cabinet's decision will then go to the full council for ratification later that day - June 7.
But campaigners say it is essential that councillors have information before them about the ecological impact of the road, which would connect the Norwich Northern Distributor Road to the A47.
The council's selected route, between Weston Longville and Ringland, would include a 720-metre-long viaduct over the River Wensum.
Campaigners say reports by Dr Charlotte Packman, of Wild Wings Ecology and Dr Mark Hassall, from the University of East Anglia's School of Environmental Sciences, provide evidence that the road would go through what could be the largest known ‘super-colony’ of barbastelle bats in the UK.
The campaign group says all councillors should be fully briefed and aware of those reports, not solely the surveys the council has commissioned, before they make their decision.
And they say a statement and commentary of those reports should be published on the council's website.
David Pett, lawyer for Stop the Wensum Link, said: "The council has had reports since February showing the route would pass through the UK’s only known super colony of the rare and highly protected barbastelle bats.
"The reports are damning – the road cannot go ahead on this route.
The council had previously said the bat roost locations information used for the Wild Wings Ecology report had not been provided to the council.
The council, which has said mitigation for bats will form part of plans for the road, previously said surveys across a wide area had been done over the past two years.
The council had said those had not recorded any barbastelle bat roosts within the scheme boundary.
We asked the council whether the reports the campaign had highlighted would be presented to councillors or if the council was disregarding them.
A spokesperson for Norfolk County Council said: "The open letter, which we received today, is lengthy and makes a number of points that we’re currently considering.
"All relevant data has and will continue to be taken into consideration on the Norwich Western Link project and our proposals will be examined through the planning process and the necessary statutory approvals.”
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here