Hundreds of homes are to be built near ancient woodland in Pershore, leading to anger from wildlife campaigners.
Worcestershire Wildlife Trust (WWT) said it had fought a long-running campaign against the scheme, but a planning inspector who reviewed the saga was "persuaded by evidence from the developer rather than Wychavon District Council's defence of the wood".
Following the inspector's decision to allow the project to go ahead, Orchard Farm near Tiddesley Wood is set for 300 new homes.
The BBC has approached developer Pegasus for comment and Formula Land, which brought the planning appeal.
Formula Land made the appeal against Wychavon District Council after the authority did not reach a decision within the prescribed period.
Steve Bloomfield, WWT senior conservation officer, called for mitigation measures to be implemented properly and to be enforced by the council.
He said: "There are two things that need to happen.
"First, it's essential that the mitigation processes are implemented properly and that the council are able to enforce those actions to make sure that the resulting harm is limited as far as possible.
"And the second thing is we absolutely must not see this as just a carte blanche for sites of this type next to other really high-value assets."
According to WWT, the land was once an enclosed deer park.
It adds that coppiced areas are "carpeted with wildflowers in spring" including bluebells, wood anemones, violets and cowslips, and are home to butterflies, insects and warblers.
Other species include the greater butterfly orchid, white-legged damselflies along with the nationally-rare noble chafer beetle.
The inspector's ruling stated development that would have an adverse effect on an SSSI (site of special scientific interest) should not normally be permitted.
It described Tiddesley Wood as ancient semi-natural woodland that was designated an SSSI in 1986.
But the ruling added: "Natural England has identified that the effects of the development are in principle capable of mitigation."
It said WWT opposed the development but the mitigation strategy included measures that were acceptable to them and they considered it the best package for limiting harm.
Councillor Nicolas Wright, chairman of Wychavon District Council's Planning Committee, said the authority had "strongly defended the district" against the proposals and found the decision disappointing.
He said: "While the inspector recognised that the proposed development would cause significant harm, they ultimately concluded that the potential benefits -- particularly the delivery of up to 300 much-needed dwellings -- outweighed these negative effects."