Biodiversity Net Gain

What is Biodiversity Net Gain (BNG)?

BNG is a new approach to planning designed to leave the environment in a better condition than it was before. In England, legislation now requires developers to improve a site’s biodiversity by at least 10% after development and maintain this gain for at least 30 years.

BNG works alongside existing wildlife and habitat laws, which remain in place. Developers still need to meet legal obligations and follow best practices, using the BNG metric to achieve better outcomes for nature. This means existing protections, statutory requirements, and the mitigation hierarchy (avoidance, mitigation, and compensation) must still be applied.

Development land newton abbot 2[paddy reardon] 141014 (a)

Why do we need BNG?

UK nature is in decline with the 2023 State of Nature report detailed that the abundance of 753 terrestrial and freshwater species has on average fallen by 19% across the UK since 1970. This is despite legislation and policies aimed at protecting nature being in place. One of the main drivers of biodiversity loss is land-use change.

In response, the government has committed to protecting 30% of the UK’s land by 2030, aiming to prevent further degradation, expand protected areas, and create new wildlife-rich habitats. Ensuring that natural spaces are not lost to development, and are instead created and enhanced, is vital for reversing species decline and meeting conservation targets.

How does BNG work?

BNG is integrated from the earliest stages of development, including site selection. Some habitats are classified as ‘irreplaceable,’ while others are marked as costly to replace due to their high biodiversity value or the time needed for them to establish. As a result, areas with lower biodiversity potential are typically chosen for development, offering a more cost-effective opportunity for achieving BNG.

After site selection, the development should be designed to maintain and enhance high-value habitats already on the site. To then achieve the mandatory 10% uplift in biodiversity, developers can take three approaches:

On-Site Habitat Creation and Enhancement: Wherever possible, the 10% gain is achieved by protecting and enhancing existing habitats and creating new ones within the development area.
Off-Site Habitat Creation and Enhancement: If on-site gains are not sufficient, developers can enhance or create habitats on nearby land or alternatively purchase biodiversity units from other landowners who have improved or created habitat.
Purchasing Biodiversity Credits: As a last resort, if neither on-site nor off-site gains meet the requirement, developers can buy government-issued biodiversity credits. These credits will be priced at a premium, with the revenue reinvested into habitat creation across England.

Biodiversity Units vs Biodiversity Credits

It is important to remember when referring to these two terms that they are distinct from one another.

Biodiversity units are the measurement used by the biodiversity metric, which assesses habitats to represent biodiversity. These units act as the “currency” of the metric. There are three types: area units, hedgerow units, and watercourse units. Units can be bought and sold if created as off-site habitat, although this is on the ‘private market’.

Biodiversity credits are the last resort option for developers, if they can’t deliver the BNG they need on-site or via purchasing off-site biodiversity units. Credits are only purchasable from the government, who sell them at a higher price than the privately sourced biodiversity units.

How is BNG measured?

BNG is measured using a biodiversity metric developed by DEFRA. This tool uses habitat types as a proxy for biodiversity value, producing a standardised score in biodiversity units. The metric assesses three modules: area habitats, hedgerows and watercourses. These modules remain distinct, for example, hedgerow loss cannot be offset by creating grassland.

The process starts with a baseline survey by a qualified ecologist, who identifies and quantifies all existing habitat types into the metric. The metric then considers factors like how unique the habitat types are, what condition they are in, and their strategic significance in the surrounding landscapes. This produces the initial biodiversity unit score, which serves as the baseline.

Habitat losses caused by the development are entered into the metric, as are the proposed habitat creation and enhancements. The biodiversity value of these new features takes into account factors like how difficult they are to create, how long they will take to reach the desired condition, and their proximity to the development site. Trading rules apply to ensure habitats are replaced on a like-for-like or like-for-better basis, meaning high-value habitats need to be compensated with the same or better-quality habitats.

The final result must meet the minimum 10% increase over the baseline score.

Baseline habitat assessment pre-development

Proposed habitat assessment post-development

How can BNG benefit Barn Owls?

Barn Owl foraging habitats currently receive no statutory protection. However, with BNG, any lost habitat must be recreated and enhanced. Ecologists working on development sites can therefore plan habitat creation tailored to Barn Owl needs, ideally ensuring habitat is provided on or as close to the site as possible and still within their home range. Strategic location planning should also help ensure these habitats are safer and more effective, for example, by locating them further away from hazards such as major roads.

BNG also provides landowners with opportunities to fund nature recovery by creating or enhancing habitats and selling biodiversity units to developers. For those who own land and are interested in supporting Barn Owls, investing in species-rich rough grassland, which is easy to create and manage, would be a great option. Rough grassland can also easily be incorporated into other habitat types such as newly establishing woodland plantations, within orchards and parklands or as field margins surrounding cut meadows.

Barow vole flight grassland [craig jones] 090819 (b)

Scrub grassland aerial [david ramsden] 190511 (a)

How do landowners participate?

Landowners interested in an additional revenue source or farm diversification can participate in BNG through creation and sale of biodiversity units. The government website goes into step-by-step detail. This is summarised below:

Consult a qualified ecologist to assess your lands existing biodiversity value. Follow local nature recovery strategies to plan habitat creation and enhancement to establish how many biodiversity units you will have to sell.
To set a price for biodiversity units, consider all costs over at least 30 years, including habitat creation, management, expert fees, and inflation. Pricing of units should be based on these expenses rather than the number of units generated, as values may vary by project location and developer needs.
To register your gain site, you need a legal agreement ensuring habitat enhancement, management and maintenance for at least 30 years is in place. This will be secured through your local planning authority or other responsible body.
Find a buyer for your units. Offsite BNG is a private market and there are numerous avenues to finding a buyer.
Sell your units, agreeing on a contract on how payment will be received for example as a lump sum or in instalments.
Once sold, units must be registered on the biodiversity gains sites register operated by Natural England. This provides transparency of where habitats have been created and prevents ‘double counting’ of units.
Units must then be allocated to an associated development, providing the local authority with evidence that BNG has been achieved.
On completion of habitat creation and enhancement works, maintenance for a minimum of 30 years begins.

It should be noted that the entire process can be completed independently or through the support of habitat bank operator that can help carry out many of the steps above.