Plans to build up to 5,000 new homes in Norfolk could be blocked after Natural England said they might threaten the habitat of a rare bird.
The government body has reassessed a series of official 'buffer zones' in the county, where building work is restricted close to sites where stone curlews are found.
Council officials say that the changes mean that 24 locations in Norfolk already earmarked for new homes may no longer be suitable.
Although councillors can still allow the developments to go ahead, they would be likely to face a legal challenge from Natural England they would likely lose.
It is the latest issue to put the organisation at odds with efforts to build new homes, after it held up housebuilding in large areas of Norfolk in a row over so-called 'nutrient neutrality'.
The areas affected by the updated stone curlew guidance are all in the Brecks, a part of the county where the amber-listed bird is found.
READ MORE: Dormitory or destination: Where next for Thetford?
The 24 locations have all been previously identified by Breckland Council for potential housing.
They are around Thetford, as well as the villages of Thompson, Foulden, Gooderstone and Cockley Cley.
If all the schemes had gone ahead, between 3,700 and 5,000 new homes would have been built.
However, they are now in doubt following the revised guidance on the number and location of homes which can be built in the buffer zones.
Sarah Suggitt, Brecklands' executive member for strategic and operational planning, said: “The Brecks is an area of significant value to bird life including stone curlews, woodlarks and nightjars and the Special Protection Area (SPA) is designed to protect this landscape.
"We are very fortunate to live and work in such a beautiful and special part of the country and this is why it is important for us to adopt this latest advice given."
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The current Thetford Sustainable Urban Expansion - a plan for 5,000 homes, schools, employment areas and health care facilities in the town - is unaffected.
Most of the schemes impacted have not yet reached the planning stage. However, there are two applications in Foulden and Thompson for 25 homes that are now affected by the regulations.
Under Natural England's guidelines, development is restricted in order to minimise the impact on the birds, which are sensitive to urban development and can be disturbed by ramblers and dog walkers.
The updated advice dictates that where an adverse effect on the SPAs cannot be ruled out, developments can only proceed if there is an overriding public interest for doing so.
It has also found that existing developments near habitats do not mask the adverse impact of any new building work, as was previously thought.
However, Natural England has stressed that its update has removed some areas from the buffer zones, making it easier for housing schemes to go ahead in those locations.
Hannah Thacker, Natural England's area manager, said: "We have recently provided updated advice to Breckland District Council regarding some small-scale developments in the area. These developments do not require an assessment of their impacts to stone curlew under the Habitats Regulations 2017.
"Natural England have also reviewed the existing 1.5km buffer zone with some areas being removed from the zone thereby reducing the need for developments in these areas to be assessed under the regulations.
"In updating the advice and removing areas from the buffer zone, the Council can now consider granting planning permission for developments where it will not adversely impact the population of stone curlew in the Breckland Special Protection Area.”
At a recent council meeting, Breckland councillors agreed to comply with Natural England’s advice and adopt the new restrictions when determining planning applications.
The changes to the stone curlew buffer zone guidance come as ministers failed to overturn Natural England's nutrient neutrality restrictions, which the organisation said were necessary to protect Norfolk’s waterways from the impact of new housing developments.
Last month, housing secretary Michael Gove came to the county to announce his plans to do away with the measures, which are said to have halted more than 40,000 homes from being built, but the House of Lords blocked the move.
The rules have been criticised by council leaders, MPs and some developers for blocking much-needed housing.
But environmentalists say they are needed to protect waterways.
READ MORE: How two words left Norfolk's plans for thousands of homes in limbo
Stone Curlews
One of the largest populations of stone curlews can be found in the Brecks and in 2006 a Special Protection Area was designated, which includes a 1.5km buffer zone around it.
The RSPB describes the summer visitor as a “strange and rare” crow-sized bird with a large head, long yellow legs and relatively long wings and tail.
It is active at night, choosing to sit still during the day to avoid the attention of predators and favours dry, open places.
It is known for its sand-coloured plumage which serves as camouflage while it nests in the sandy heaths and open grounds of East Anglia.
Its numbers have declined, reaching a low point in the 1980s but conservation efforts have meant breeding numbers have more than doubled.
Most migrate for the winter but they are increasingly leaving late and returning early.
Despite sharing the same name, they are of no relation to curlews.
How animals have put a spanner in the works for major Norfolk developments
This is not the first time that protected species have frustrated planners and prompted changes to developments.
Hopes to dual the A47 Acle Straight were thrown into doubt due to minuscule molluscs living along the roadside.
Dykes around the road are one of the few habitats of the Little Whirlpool Ramshorn Snail - which is on an international 'red list' of endangered species.
It meant that no work could go ahead until they were removed and a five-year study was then conducted to determine if the snails recovered after the relocation.
Bats put brakes on another major road development – the Western Link – which forced the route to be changed.
Rare barbastelle bats living in woodlands in the lower Wensum Valley prompted the Norfolk Wildlife Trust to object to the plans, saying the road would be “catastrophic” for the super colony.
The ongoing Western Link saga has cost the council £40 million before a spade has even gone into the ground.
In Great Yarmouth, a phantom vole pushed back the opening of the new £121m river crossing after builders found evidence the small mammal was living near the structure.
It meant the Herring Bridge did not open in time for the town’s main summer tourism season, as originally planned.
And in Hellesdon, developers were left scrambling to make last-minute changes to a major housing application after newts were discovered in a neighbouring property’s garden.
Persimmon Homes were forced into late amendments to the plans to ensure the welfare of the slippery amphibians were accounted for.
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