The government’s justification for retaining a key exemption from England’s Biodiversity Net Gain rules is built on examples of developments that would not have needed to comply with the policy in the first place, according to a new briefing.
Wildlife and Countryside Link and The Wildlife Trusts are challenging the government’s decision to keep the so-called de minimis exemption, which allows developers to self-declare that their project has ‘low-to-no’ impact on biodiversity and therefore opt out of the requirement to deliver a 10% net gain. Officials cited four types of development to justify retaining the exemption but the briefing argues that each one is a red herring.
The first example, change of use applications such as converting a warehouse to offices, involves minimal physical works to land and therefore generates little or no measurable habitat impact. The BNG system would already handle such cases without any exemption being needed.
The second, installing solar panels on an existing industrial rooftop, involves no ground-level habitat change whatsoever, and many such installations do not even require a planning application.
A third example – replacing a petrol station with an EV charging point – involves hardstanding that already scores zero in the statutory biodiversity metric, meaning BNG would not apply anyway.
The fourth, adding storeys to an existing block of flats, does not extend a building’s footprint into surrounding land and so leaves the biodiversity baseline of the site unchanged.
In each case, the briefing concludes, the existing mechanics of the BNG system already deal with genuinely low-impact development without any need for a separate self-declaratory exemption.
The concern is that in practice the de minimis route is being used far more widely. Analysis by economics consultancy eftec, drawing on Planning Portal data from BNG’s entire first year, found that 86% of the 101,728 planning applications submitted between March 2024 and February 2025 claimed some form of BNG exemption, with more than half specifically using the de minimis route. Around 35% of developments on sites larger than half a hectare also claimed the exemption, a scale that analysts described as ‘not credible.’
The groups estimate that an area equivalent to the city of Manchester is currently being lost to development annually with no obligation to offset a single biodiversity unit. If the de minimis exemption were closed, they argue, an area the size of the Isle of Wight could be brought back into scope each year.
Wildlife and Countryside Link is calling for the exemption to be removed, arguing that a system promising net gain should not be delivering the systematic, unmeasured loss of habitats.
The full briefing can be read here.