Biodiversity Net Gain | What is it and what does it mean for development in the UK?

VERSION 2 | Updated on January 1st, 2024


What is BNG?

In this section read more about:
  • Why does it matter?
  • How Biodiversity Net Gain will be achieved through the new Environment Bill?
  • Who is exempt from Biodiversity Net Gain?

What is Biodiversity Net Gain (BNG) and why does it matter?

Biodiversity Net Gain is a sustainable approach to development and land management that intends to ensure that development projects have a positive impact on biodiversity. The idea is that any development should not just avoid harm to nature but contribute to its restoration and enhancement, leaving the natural environment in a measurably better state than it was beforehand.

In the new Environment Act 2021, the UK government introduced a mandatory biodiversity net gain environment bill (which will start to be effective November 2023) making biodiversity net gain a legal requirement for all new developments in England. To secure planning permission, developers will have to submit a Biodiversity Gain Plan (BGP), assessing the habitat value of the land they will be developing and providing a measurable plan of how they will create a net uplift in biodiversity of at least 10% over a minimum period of 30 years.  

This new approach addresses the significant and ongoing biodiversity losses, specifically those losses caused by human action. It seeks to counteract these losses by requiring that any new developments or builds improve the overall biodiversity value in existing habitats or by generating additional biodiversity gains through measurable improvements.

How Biodiversity Net Gain will be achieved through the new Environment Bill

Property Developers, Local Planning Authorities, and Landowners/Homeowners will all be required to do their bit to achieve the Biodiversity Net Gain goals outlined in the UK’s Biodiversity Net Gain Environment Bill.

To be allowed to commence developments, property developers will need to prove that their development will enhance biodiversity, or achieve net gain, by meeting the minimum requirements outlined in the UK's new biodiversity net gain approach (a 10% biodiversity net gain expectation over the next 30 years). Development proposals must now include a Biodiversity Gain Plan, or BGP for short. There are three avenues by which biodiversity value can be incorporated into a development proposal to meet the new requirements.

  1. Creating on-site environmental benefits that enhance the habitat value directly (preferable)

Examples of this may be - enhancing wildlife habitats in a way that will safeguard protected species, building green infrastructure, and/or contributing to local nature recovery strategies with ecological importance. In doing so, developers will be improving air quality, providing access to green space and nature, building for flood resilience, protecting priority habitats, preserving irreplaceable habitats, incorporating ecological features into future developments, and many other environmental management benefits to improve biodiversity!

  1. Registering an off-site net gain that has been allocated and approved as part of the development project (acceptable in the case it is not possible to create biodiversity net gain on-site)

This off-site property can be owned by the developer or permitted for use by a separate landowner. Examples listed in the on-site habitat biodiversity gain options above would also apply to these off-site allocations.

  1. Obtaining statutory biodiversity credits from the Secretary of State in accordance with the environment bill requirements (not preferred and only applicable in special cases)

This third option has been established as a last resort to reach biodiversity net gain mandates in the case developers are unable to achieve biodiversity net gain minimum requirements on-site or off-site.  

To create biodiversity credits, the UK government will establish biodiversity enhancements throughout the country, all focused on delivering biodiversity net gain. Every enhancement project or land parcel will have a biodiversity value or “credit”. These biodiversity credits may then be purchased as part of a Biodiversity Gain Plan to deliver net gain minimums.

All payments from biodiversity credits to the Secretary of State will be utilised solely for the purpose of habitat enhancement. This can include acquiring land interests, carrying out necessary works, and covering operational and administrative expenses associated.

Local Planning Authorities have the legal obligation to assess the Biodiversity Gain Plan (in addition to all other required documents) as a part of the approval process to grant development permissions. As the planning authority in each local council, it is their responsibility to prevent biodiversity loss for all new and future developments. To this end, it’s important that they know how to “measure biodiversity” and can accurately evaluate how new developments will be delivering net gain on and off development sites.

Landowners and homeowners have the opportunity to assess their property for its habitat value, offering off-site biodiversity units that developers may purchase in cases where they are unable to meet the minimum biodiversity net gain on-site.

BNG principles for development

Beyond merely offsetting losses, Biodiversity Net Gain aims to prevent further biodiversity loss by preserving local habitats, engaging stakeholders, and aligning with local and national conservation aims. Maintaining and reversing biodiversity loss will require massive collaboration. To facilitate these underlying goals, the following 10 principles have been developed by CIEEM, IEMA and CIRIA to ensure a comprehensive and effective approach to achieving sustainable and meaningful Biodiversity Net Gain.

  1. Apply the Mitigation Hierarchy: Prioritise avoiding environmental harm, followed by minimising impacts, then remediation. Where harm is unavoidable, compensate through environmental enhancements.

  1. Avoid losing irreplaceable biodiversity: Protect habitats and species that cannot be replaced or replicated elsewhere.

  1. Be inclusive and equitable: Involve and consider all stakeholders, ensuring fair distribution of environmental benefits and burdens.

  1. Address risks: Anticipate and manage potential negative impacts on biodiversity throughout the project lifecycle.

  1. Make a measurable Net Gain contribution: Quantify improvements in biodiversity, ensuring gains outweigh losses.

  1. Achieve the best outcomes for biodiversity: Aim for high-quality, sustainable ecological improvements that support a diverse range of species and habitats.

  1. Be additional: BNG initiatives should enhance, not replace, existing biodiversity commitments and regulations.

  1. Create a Net Gain legacy: Develop long-term, sustainable benefits for biodiversity, leaving a positive impact for future generations.

  1. Optimise sustainability: Integrate BNG with broader environmental sustainability goals, creating synergy between biodiversity and other ecological targets.

  1. Be transparent: Maintain openness in all BNG processes and decisions, ensuring accountability and public trust.

Key components of mandatory Biodiversity Net Gain

The Environment Act 2021 mandates the key components for Biodiversity Net Gain for all new developments (with very few exceptions). It revises the Town & Country Planning Act originated in 1990 and stipulates the following requirements:

  • Minimum Biodiversity Gain: A mandatory increase of at least 10% in biodiversity is required, with this gain quantified using the established Biodiversity Metric (the Government can change the percentage if it wishes).

  • Long-term Habitat Protection: Newly developed habitats must be safeguarded for a minimum duration of 30 years. This protection is ensured through planning obligations or conservation covenants.

  • Flexible Achievement of Biodiversity Net Gain: The strategy for achieving Biodiversity Net Gain is flexible, allowing for implementation either on-site, off-site, or through a statutory biodiversity credits scheme - though, in accordance with the mitigation hierarchy, restorative work should always be as close as possible to the point of impact.

  • National Register and Existing Protections: The Act introduces a national register for tracking net gain delivery sites.

  • Retention of Current Legal Protections: The Act maintains existing legal safeguards for key habitats and wildlife species, ensuring that these areas continue to receive the protection they currently enjoy.

  • Adherence to Mitigation Hierarchy: As noted above, a clear emphasis is placed on following a mitigation hierarchy. This involves a prioritised approach where the first step is to avoid environmental impacts. If avoidance is not possible, the next step is to mitigate these impacts. Compensatory measures are considered only as a last resort.

  • Scope of Application: The Act's provisions are applicable to many types of development including Nationally Significant Infrastructure Projects (NSIPs).

The sooner the better - why getting involved with Biodiversity Net Gain now is valuable

Councils and many developers are already gearing up for the impending legal requirements of Biodiversity Net Gain, and there are numerous advantages to staying ahead of the legislation. Understanding and integrating Biodiversity Net Gain into current and future projects not only provides a head start in complying with future legislation but can also aid developers in better managing and coordinating their projects in line with local conservation efforts and evolving requirements.

Beyond policy compliance, Biodiversity Net Gain is an opportunity for councils to think holistically, linking Biodiversity Net Gains with broader council services. For councils that have declared a climate and ecological emergency, Biodiversity Net Gain offers a tangible action to address these crises. It's a chance to envision and shape the future natural environment of local areas, ensuring it delivers for the community.

Local Nature Recovery Strategies (LNRS) are another critical aspect. They offer an opportunity for collaborative work with neighbouring authorities’ reach beyond local government to involve communities, landowners, developers and farmers in creating and reaping the benefits of Biodiversity Net Gains, particularly when it comes to biodiversity units (BUs) in the off-site BU credit market.

Engaging with Biodiversity Net Gain now also allows for input into ongoing policy development by Defra and Natural England. Early adoption of  Biodiversity Net Gain practices can inform policy and legislation, making them more effective and applicable.

Who is exempt from Biodiversity Net Gain?

The UK Government has listed a small number of exemptions from the Biodiversity Net Gain (BNG) rules. However, it’s worth saying that these exemptions are few and far between - BNG is intended to be a universal policy, and it’s always better to err on the side of complying than trying to avoid. That said, let’s look at the exemptions: 

De Minimis Threshold: Designed for the smallest of projects, if a development impacts no priority habitat and less than 25 square metres of non-zero rated habitat, or less than 5 metres for linear habitats like hedgerows and watercourses, it will fall below the 'de minimis' threshold and will be exempt from BNG. However, you must demonstrate that you are genuinely eligible to meet the de minemis threshold and the Local Planning Authority will inspect any claim to ensure that there is no fraudulent attempts to sidestep the new obligations. 

Householder Applications: Development related to household applications also falls under the exemptions. Of course, you can always undertake BNG anyway or there are a number of other things you can do to increase biodiversity in your home.

Self-Build and Small-Scale Developments: Small scale self-build and custom housebuilding projects are included in the exemptions, however you must make sure that you meet the specifications set out in the relevant laws. 

Biodiversity Gain Sites: Sites specifically enhanced to benefit wildlife, termed biodiversity gain sites, are exempt (these sites are already geared towards enhancing biodiversity, they are not subject to additional BNG requirements). 

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Calculating BNG

In this section read more about:
  • What exactly is Biodiversity Metric 4.0?
  • Who is the biodiversity metric for?
  • How it’s necessary to calculate BNG?

Running a biodiversity net gain assessment - calculating biodiversity net gain

The Biodiversity Metric is the key tool that supports the delivery of Biodiversity Net Gain. Under the new law, this is what developers will have to use to assess what impact their development has on local biodiversity. It is a habitat based approach used to assess an area’s importance and value to the ecosystem on the site to be developed. The biodiversity metric uses habitat features to measure the biodiversity value and calculate the biodiversity units present on-site. It can be used by (among others):

  • Property Developers creating biodiversity gain plan
  • Local Planning Authorities who are interpreting metric outputs in a planning application
  • Landowners, homeowners or land managers who want to provide biodiversity units from their sites to others
  • Communities who want to understand the impacts of a local development

An original and basic version was developed by the Department for Environment, Food and Rural Affairs, known as the DEFRA biodiversity metric. However, more recently DEFRA has paired up with Natural England to create the Biodiversity Metric 4.0 which is the new standard and the DEFRA approved biodiversity metric. It is used to calculate the baseline biodiversity value of a site and forecast its future biodiversity value. It will help ensure there will be no biodiversity loss, only net gains.

While Biodiversity Metric 4.0 is the current project development standard, the choice of a metric may depend on the specific needs of the development project and the available data. Small property developers have the option to use the small sites metric and user guide which are both published on Natural England’s website.

What exactly is Biodiversity Metric 4.0?

Natural England describes Biodiversity Metric 4.0 (BM 4.0) as “a biodiversity accounting tool that can be used for the purposes of calculating net gain”. Under the new Environment Act 2021, the UK government introduced a mandatory biodiversity net gain obligation (which will start to become effective from November 2023) making Biodiversity Net Gain a legal requirement for nearly all new developments in England. Biodiversity Metric 4.0 is THE KEY TOOL that supports the delivery of the biodiversity net gain obligation, and its use will be compulsory. It’s important to understand it!

So what exactly is this tool? Biodiversity Metric 4.0 was designed to provide a standardised approach to assessing the biodiversity impact of development projects, and to ensure that the impact is fully accounted for and compensated for. In other words, no matter where you are in England, the tool ensures biodiversity is measured in the same way. We’ve touched on this in other blogs but to briefly review, Biodiversity Net Gain requires that any new development will be required to submit a Biodiversity Gain Plan that accounts for their on-site biodiversity score pre development and details how they will provide a minimum net gain of 10% to that biodiversity over the next 30+ years.

Natural England, along with the Department for Environment, Food & Rural Affairs (DEFRA), created Biodiversity Metric 4.0 as a habitat based approach to measuring a site’s biodiversity and then appraising the area’s importance and impact to the ecosystem at large. Biodiversity Metric 4.0 uses habitat features to assess the site’s value. This is based on a set of ecological characteristics that are important for biodiversity, such as habitat quality, condition and location. These habitat characteristics are used to assign a score to the site, counted in biodiversity units (BUs), which reflects its overall biodiversity value. The biodiversity units are then used to determine the net gain or loss in biodiversity resulting from a development.

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Joe’s Blooms BNG Case Study

In this section read more about:
  • New biodiversity laws set to secure over 23,500 football fields worth of natural habitat in England each year
  • Research Methodology
  • Data Summary

New biodiversity laws set to secure over 23,500 football fields worth of natural habitat in England each year

About Biodiversity Net Gain

‘Biodiversity Net Gain’ (BNG) requires property developers to invest in measures that increase the amount of plants and wildlife in the local area by 10%, making UK towns and villages greener and helping to support nature recovery.

Due to start to come into effect this November, the new statutory requirements are part of the 2021 Environment Act and require property developers to fill a biodiversity metric and produce a ‘Biodiversity Gain Plan’ (BGP). Once ready, the BGP must be approved by the Local Planning Authority (LPA) in order to allow development to begin.


The Government’s publicly available Net Gain Impact Assessment found that the key natural capital benefits of the ‘Net Gain’ policy are derived from habitat loss avoided and habitat created:

1. Government figures show that 5,428 ha of habitat would be created per year, and 9,644 ha per year of habitat damage would be avoided per year (p.37 of the Net Gain Impact Assessment, link).

2. We calculated football field size by taking the minimum permitted size for international games as set out in the IFAB Law of the Game (6,400m2, link).

3. We combined the Net Gain Impact Assessment figures with  Government estimates for total development per year to calculate the avoided habitat loss / habitat creation for each ha developed (HM Government, November 2019, p.36, link).  According to this, 16,232 ha total development per year will result in:

               a. 0.5941 avoided habitat loss for each ha developed
               b. 0.3344 habitat created for each ha developed

4. To calculate the figures for each LPA, we used ONS data on the  number of planning decisions and size of developments in  each LPA to calculate the total ha developed in each LPA each year (link). We then multiplied the total area developed in each LPA with the equivalent values in point 3 (a) and (b) to calculate the increase in biodiversity in each LPA each year.

The impact of BNG on English regions and top 10 metropolitan areas is below. These calculations are based on figures and estimates from 2021.

Table 1: Natural habitat secured by region
Table 2: Natural habitat secured by metropolitan areas

In summary

  • New analysis reveals that the Government’s Biodiversity Net Gain (BNG) laws will secure over 15,000 hectares, or 23,500 football pitches, worth of biodiversity in England each year.
  • Set to come into effect this November, BNG requires property developers to invest in measures that increase the biodiversity score of sites by at least 10% as part of the planning process.
  • This policy will boost natural habitat across the country, with data showing the biggest uplifts experienced in the South East and East of England across the regions.
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Mitigation hierarchy: offsetting biodiversity loss

In this section read more about:
  • Why mitigation hierarchy is a crucial framework for?
  • What are biodiversity offsets?
  • Who is exempt from Biodiversity Net Gain?

Mitigation Hierarchy, planning and proving biodiversity net gain

In addition to the biodiversity metric, mitigation hierarchy is a crucial framework and should be used to outline a set of steps to reduce, mitigate, or offset the negative impacts of development on biodiversity. The hierarchy consists of four main steps:

  1. Avoidance involves selecting development sites that have the least negative impact on biodiversity
  2. Minimisation involves reducing the negative impact of development on biodiversity
  3. Restoration involves restoring the affected habitats to their original state or improving their quality
  4. Offsetting involves creating new habitats or enhancing existing ones to compensate for the loss of biodiversity resulting from development

Biodiversity Offsets for planning and development permissions

Biodiversity offset policies have become an increasingly popular strategy for mitigating the impact of development on natural ecosystems around the world. While it is always preferable to try and avoid and minimise damage to biodiversity, sometimes it’s simply unavoidable - and when that happens biodiversity offsets offer a mechanism for balancing the impact of development through ecological compensation (restoration, enhancement, or protection of ecosystems) in other locations. In this blog, we will explore what biodiversity offsetting is and how it may be implemented into Biodiversity Gain Plans to meet new UK national policy to preserve and protect biodiversity.

How do Biodiversity Credits Work?

Biodiversity Credits will be a key part in the new Biodiversity Net Gain (BNG) regime. They will help to ensure that development projects comply with the new BNG rules so that when - and only when - it isn't possible to offset biodiversity losses from environmental projects, there is an ultimate fall back. Biodiversity Credits are the ‘in emergency break glass' option that will help ensure that every development can comply with biodiversity conservation outcomes under the new rules.

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Securing a 10% biodiversity uplift with a BGP

In this section read more about:
  • Guidance to secure your Biodiversity Net Gain Plan
  • What is included in a Biodiversity Net Gain Plan?
  • How Joe’s Blooms tools help streamline the biodiversity net gain planning process

Guidance for Biodiversity Net Gain Plans

Biodiversity net gain assessments and mitigation hierarchy structures are essential to developing a biodiversity gain plan. The use of Biodiversity Metric 4.0 and application of the mitigation hierarchy are both necessary to prove biodiversity net gains and get a biodiversity gain plan approved.

Biodiversity Net Gain policy stipulates a framework of requirements. Standards around what needs to be included in a biodiversity gain plan are currently scattered across different resources, legislation and government publications. You may be familiar with The DEFRA Biodiversity Metric as a common metric in the UK. However, it's recently been updated and replaced by the Natural England Metric 4.0 (or Small Site Metric, where applicable). Despite the complexities and ambiguities, compliance is strict and ALL the requirements set out in the Environment Act must be fulfilled and approved by the local planning authority. Given the complexities of different sites, the natural habitats existing on them, and the needs of each development project, there are a number of resources and expertise needed to develop a thorough and accurate Biodiversity Gain Plan.

It will require a calculation of the development site’s biodiversity metrics, and a mitigation hierarchy to prove how the development will be delivering a minimum 10% biodiversity net gain over the next 30+ years -  all collated into a biodiversity gain plan.

Here’s a basic outline of what should be considered and/or included in a Biodiversity Gain Plan:

Site survey: A preliminary appraisal of the existing biodiversity on the site, including a survey of the habitats present. This is the first step to understanding the habitat’s biodiversity value and is essential for calculating the biodiversity net gain needed for planning approval by local authorities.

Biodiversity goals: A set of clear, measurable objectives for delivering biodiversity net gains. This could include specific targets for increasing the number of biodiversity units by creating new habitats.

Habitat creation / restoration plans: A plan for restoring any existing habitats on the site that have been damaged or degraded by past activities. This may involve removing invasive species, improving soil quality, planting new vegetation, or including any other biodiversity net gain of special scientific interest.

Mitigation measures: A plan for reducing the impact of the development on the site's biodiversity. This may involve measures such as wildlife corridors, green roofs, or green walls.

Monitoring and reporting plans: A plan for monitoring the success of the biodiversity gain plan and reporting progress to the relevant local planning authorities. This may involve regular surveys of the site's flora and fauna, and regular reporting on progress towards biodiversity net gain goals.

Financial commitment: A clear commitment to funding and implementing the biodiversity gain plan over the 30 years. This may involve setting aside a portion of the development budget specifically for biodiversity net gain enhancement measures.

Cost effective resources for biodiversity net gain planning

There’s a plethora of free information as well as paid consultants available for completing the statutory Biodiversity Net Gain Metric and for researching and writing a Biodiversity Gain Plan. It can be a daunting and an expensive endeavour. That’s why Joe’s Blooms has built a self-service digital platform to simplify and streamline the process. Our online platform service helps by providing a digital end-to-end solution. It allows developers to collate all the necessary information about their site, inputs this data into a biodiversity metric tool, and then generates a Biodiversity Gain Plan that meets all the statutory requirements for biodiversity net gain planning approval.  Our solutions are fully compliant with the law and embed best practice at each stage. They help ensure that small developers who lack resources are still given the tools and chance to ‘go green’. So long as the data entered is an accurate reflection of what is on the site, the material that our tool produces will meet all your needs.

Using a digital tool like Joe’s Blooms helps small developers save time on researching the finer details of regulations and compliance while cutting the costs of expensive consultants. The investment in our digital resource for biodiversity net gain compliance could save you tens of thousands of pounds on consultation costs.

Joe’s Blooms is already working with a number of stakeholders, including DEFRA and Natural England, to ensure our system and solutions fully comply with the 'Net Gain' policy. For the purposes of demonstrating a proof of concept, the first version of Joe’s Blooms’ product uses the Biodiversity Metric 4.0.

You can keep up to date with us by subscribing to our news and updates here.

The implications of biodiversity net gain for developers and landowners is huge and failing to deliver adequate biodiversity net gain could be a time consuming and costly error. Our platform service is designed and vetted to make developing a biodiversity gain plan as fast and easy as possible, so you can get on with your development.

Get in touch with us today to see how we can directly help you with your biodiversity net gain plan.

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Oliver Lewis

Founder of Joe’s Blooms

Oliver Lewis is the founder of Joe’s Blooms, providing end-to-end digital solutions to help you create best-in-class Biodiversity Gain Plans. Expert in this field, he shares his knowledge on the Environment Bill.

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