The Middlewick Ranges, an army firing range near Colchester, Essex, has been untouched by agriculture for nearly 200 years, allowing endangered species to thrive in the rare acid grassland.
Under DEFRA’s biodiversity metric, developers can build on some types of rare land, including fens, wetland and woodland, so long as they offset the loss by creating replacements.
But Richard Martin, from the Save the Middlewick Ranges group, told the Guardian that under this metric the score is too high to allow development.
Instead, he said, the MoD “came up with their own one”.
The MoD’s property arm, the Defence Infrastructure Organisation (DIO), agreed the use of a “bespoke metric” with Colchester Borough Council to push through outline permission to develop the 86 hectare (215-acre) site under the plan.
Campaigners are also dismayed that the MoD is proposing to replace the acid grassland, by converting farmland nearby.
“They want to put sulphur into the land,” Martin said. “There’s a little brook that runs next to it and all the lands drain into that brook.
“And that flows into Colne Marshes, which is a site of special scientific interest. So you’re going to put sulphur in the rainwater that flows into a SSSI wildlife site.”
The campaigners have been backed by Essex Wildlife Trust, which has said it “cannot afford to lose” the Middlewick Ranges.
The campaigns resulted in a planning inquiry into how the ranges were added to the local plan, which concluded its hearings earlier this year.
Rosie Pearson, a founder of the Community Planning Alliance, which has advised the campaigners, told the Guardian that developers have been manipulating biodiversity offsetting calculations.
She said ecological assessments should be done by an independent body, funded by developers.
“Local communities should be able to request a second opinion, also funded by the developer, if they have concerns about a report. And government proposals to provide better funding to local authorities for ecology services should be followed through,” she added.
The MoD has defended its plans, saying 63% of the land would be reserved for green open space.
It has yet to sell the site to a developer, who would still need planning permission, but if the plan is upheld, opposition would be limited to discussing which parts of the ranges could be built on.
A spokesperson for Colchester Borough Council said: “Whilst we are unable to comment on DIO’s specific plans for the site, the council remains fully committed to preserving and enhancing all forms of biodiversity in the borough to the greatest extent possible.”
The MoD said: “We continue to work with the council to develop plans for the site, including working with experts to find innovative means to help secure biodiversity. The techniques will be thoroughly tested as part of the examination process.”