Biodiversity Net Gain
Since February 2024, most development in England must leave nature in a better state than it found it. Here's what that means in practice.
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What is Biodiversity Net Gain?
Biodiversity means the variety of life. Not just the number of species, but the diversity within species, between species, and across entire ecosystems. A species-rich woodland with varied age structure and abundant deadwood has high biodiversity. A grass monoculture (one species planted uniformly across an area) has low biodiversity.
Net Gain means achieving a measurable increase. Not just replacing what was lost. Not mitigating damage. Actively improving.
Since February 2024, most development in England must deliver a 10% biodiversity net gain (BNG). This means leaving biodiversity in a measurably better state than before construction began.
This applies to housing estates, commercial buildings, infrastructure projects, and nearly every other form of development that requires planning permission. The few exemptions include small household extensions and some permitted development rights.
How BNG Works
Development impacts are measured by the Department for Environment, Food and Rural Affairs (DEFRA) and Natural England, the government's adviser for the natural environment. They calculate biodiversity value based on:
Habitat type - A hectare of ancient woodland scores far higher than a hectare of amenity grassland.
Habitat condition - Well-managed species-rich grassland delivers more units than degraded, species-poor grassland of the same type.
Strategic location - Habitats that connect to nature recovery networks or local priority areas receive higher scores.
Habitat creation or enhancement must be legally protected for at least 30 years. This protection uses formal agreements (such as a Section 106 planning obligation or a conservation covenant) that bind future landowners. Annual monitoring reports prove the habitats are delivering what was promised.
The 10% Requirement
These factors are converted into standardised biodiversity units - a scoring system that puts a number on nature's value.
A development might lose 50 units of habitat. To achieve 10% net gain, developers would need to create or enhance habitat worth 55 units or more.
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The State of UK Biodiversity
According to Natural England's 2023 assessment, only 14% of England's habitats are in good ecological condition. We've lost 97% of our wildflower meadows since the 1930s. Hedgerow networks have been halved. Wild bee populations have crashed by over 50% since the 1980s, with knock-on effects for crop pollination and food security.
Development has historically made this worse. For decades, planning policy required developers to avoid harm where possible and mitigate unavoidable impacts, but the net result was still habitat loss. Even well-intentioned "no net loss" policies failed to reverse the trend.
BNG changes this. For the first time, the planning system actively requires biodiversity increase rather than simply slowing its decline.
Why Biodiversity Specifically Matters
BNG isn't just about creating "more nature". It's about creating the right kind of nature - structurally complex, species-rich habitats that deliver outcomes mown lawns and monoculture plantings cannot.
Ecosystem function - Biodiverse woodlands with varied age structure store more carbon and support more complex food webs than single-species plantations. Species-rich wetlands regulate water flow and reduce flooding more effectively than simple drainage channels. These functions depend on biodiversity, not just greenery.
Human wellbeing - Research from King's College London found that exposure to biodiverse environments - with varied trees, plants, birds, and water features - produces measurably better mental health outcomes than exposure to simple green spaces. A 2024 study of 15,000 households found people living near biodiverse areas reported lower rates of depression and anxiety, even after controlling for socioeconomic factors. The diversity itself matters.
Species under threat - England has lost viable populations of hundreds of species in the past century. BNG creates habitat networks that allow wildlife to move, breed, and persist. Isolated populations face genetic bottlenecks and local extinction. Connected, high-quality habitat gives species a fighting chance.
The Environment Act estimates BNG will create over 15,000 hectares of new or improved habitat each year. That's roughly the size of Manchester. Plus Bath. Habitat with legal protection, long-term management, and measurable biodiversity value secured permanently.
The Three Routes to Compliance
BNG follows a strict hierarchy. Developers must consider each option in order.
1. Onsite Enhancement
Create or enhance habitat within the site. This might mean:
- Retaining existing hedgerows and improving their structure
- Converting regularly mown grass to species-rich wildflower meadows
- Creating ponds or restoring ditches and streams
- Planting native woodland or scrub on land unsuitable for building
For detailed guidance on creating specific habitats, see our BNG Habitats Directory with management advice for each habitat type.
Onsite delivery is preferred because it keeps habitat close to where it was lost, but many developments lack sufficient space or suitable conditions to deliver all 10% onsite.
2. Offsite Units
Purchase biodiversity units from registered habitat banks. These are dedicated sites where landowners create or restore priority habitats specifically to generate BNG units.
Each scheme must:
- Have a detailed habitat management plan covering 30 years minimum
- Be registered on Natural England's Biodiversity Gain Sites Register
The system prioritises sourcing units close to where habitat was lost. Units purchased from further away are worth less, meaning you need more of them - so buying locally is nearly always cheaper as well as ecologically preferable.
Offsite units can be purchased before planning submission, giving developers certainty they can meet BNG requirements.
3. Statutory Credits
If neither onsite nor offsite options are feasible, developers can buy government-backed credits. These are priced deliberately high (currently from £42,000 to £650,000 per unit!) to discourage their use, and require written justification to the local planning authority explaining why local offsite units couldn't be secured.
Delivering Quality Outcomes
The legislation includes safeguards to ensure high-quality outcomes:
Irreplaceable habitats cannot be offset - Ancient woodland, blanket bog, limestone pavement, and other irreplaceable habitats are protected. If you destroy them, no amount of habitat creation elsewhere compensates.
Trading rules prevent downgrading - Losses must be replaced on a "like-for-like or better" basis using the same or higher quality habitat types.
Long-term monitoring and enforcement - All BNG delivery is monitored annually. If habitats fail to reach target condition, remedial management must be undertaken. This obligation stays with the land permanently, binding on all future owners.
Local Nature Recovery Strategies - Maps being rolled out across England that show where habitat creation will have the greatest impact on nature recovery. BNG schemes in these priority locations score higher.
The system is designed to reward high-integrity, well-located habitat creation whilst making it difficult to game the rules.
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Additionality
All BNG - whether onsite, offsite, or statutory credits - must be additional. This means the biodiversity improvements must genuinely add to what would have happened anyway.
You cannot claim BNG credit for:
- Habitat that already exists in good condition
- Improvements you're already legally required to make (e.g. under environmental permits, agri-environment schemes, or planning conditions from previous developments)
- Management that would happen regardless (e.g. a farmer who was planning to rewild a field anyway)
FAQs
BNG is mandatory for most planning applications submitted after 12 February 2024 (major developments) or 2 April 2024 (minor developments). Small household extensions, some agricultural buildings, and certain types of development that don't need planning permission are exempt. If you're unsure, check the government's BNG exemptions guidance or consult a planning specialist.
An ecologist surveys your site and calculates how much biodiversity you have now and how much you'll have after development. They produce a biodiversity gain plan which must be approved by your local planning authority before development can begin.
Yes. Some developers secure offsite units or establish onsite habitats early to give planning committees confidence that BNG can be delivered.
BNG costs vary widely depending on site context and delivery route. Offsite units typically cost £15,000-£40,000 per unit. Some developments can reduce offsite requirements through intelligent onsite design. If genuinely unviable, applications will be refused.
All BNG sites are monitored annually - by a Responsible Body if secured through a conservation covenant (a private agreement that binds future landowners), or by the Local Planning Authority if secured through a Section 106 agreement (a legally binding planning obligation). Offsite sites must also be listed on Natural England's public register.
If obligations are breached, the monitoring body can take enforcement action. Developers who purchase offsite units transfer the long-term management responsibility to the habitat bank operator.
The Bigger Picture
BNG is part of a broader policy shift recognising nature as essential infrastructure rather than optional "green space". It sits alongside Nutrient Neutrality, Local Nature Recovery Strategies, Environmental Land Management schemes, and the government's target of protecting 30% of UK land for nature by 2030.
This represents a fundamental change in how development interacts with the environment. Rather than treating nature as something to work around or minimise harm to, the planning system now requires active contribution to biodiversity recovery.
For developers, this means integrating ecological expertise early in the design process. For landowners, it creates opportunities to diversify income whilst delivering environmental benefits. For ecologists and conservationists, BNG changes the game. For the first time, the planning system demands improvement, not just damage limitation.
The evidence is clear: business-as-usual has failed to stop biodiversity decline. BNG is the planning system's answer to that failure. Whether 10% proves sufficient remains to be seen, but it's an evidence-based start backed by statutory obligation, robust methodology, and long-term legal security.
Getting Started
Whether you're a developer navigating BNG requirements or a landowner considering creating a habitat bank, understanding the rules is essential.