Natural England has been threatened with legal action by a Norfolk ecologist, who has accused the body of failing in its duty to protect a rare species of bat.

It comes two weeks after Norfolk County Council had to suspend bat surveys on the route of the proposed Western Link Road following an intervention by Natural England.

The body later issued a modified licence allowing the council’s contractors to begin the survey this month, despite concerns it could be a disaster for the woodland’s barbastelle bats and their pups.

Ecologist Dr Charlotte Packman, of Norwich Research Park-based Wild Wings Ecology, called the amendment a “watering down” of the licence and has now written to Natural England.

In a letter to bosses, lawyer David Pett wrote on her behalf: “On the basis of evidence [Dr Packman] has collected, and with regard to well and widely established bat welfare standards, she has good cause to believe that Natural England has failed in its statutory duty as a licence issuer to provide adequate protection for the bats.”

The letter says in the light of “possible litigation” and the “well-grounded fear of a real and imminent risk to death of these protected bats”, no bat trapping and/or radio-tagging surveys should be undertaken until after August 15.

Dr Packman, added: “It is still too early. Anytime in July is too early it should be safe from the beginning of August. I know that is not long but a week is quite a long time in the development of the pups. “

Ryan Hildred, Natural England wildlife licensing service manager, said: “The protection of these bats is our top priority. After receiving evidence that the bats in this area of Norfolk have different mating habits than other populations nationally, we issued an amended licence to ensure the ongoing protection for both them and their pups.

“Following a further assessment of the licence application we have issued another modified licence which allows the survey to take place this month – while ensuring strict conditions of the capturing of bats to ensure their wellbeing.”

“Natural England has considered the application and the risks carefully, and in our judgement, we are content with the licence and the conditions as issued.”

Norfolk County Council has previously said it had discussed the licence revision with Natural England, and would work with the body on taking future steps.