BNG ASSESSMENT

A Biodiversity Net Gain (BNG) Assessment measures changes in the biodiversity value of habitats resulting from development or land-use change. For developments subject to mandatory BNG under the Town and Country Planning Act regime in England, the Statutory Biodiversity Metric is used to calculate biodiversity units and demonstrate whether the required minimum 10% biodiversity net gain has been achieved.

At Tunley Environmental, we deliver BNG Assessments by evaluating baseline site conditions, calculating biodiversity units across habitats, hedgerows, and watercourses, and developing practical strategies to achieve the required net gain through habitat creation, enhancement, restoration, and offsetting where necessary.

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Cultivating A Greener Tomorrow

WHAT IS BIODIVERSITY NET GAIN?

A Biodiversity Net Gain Assessment measures the biodiversity value of habitats before and after development, using habitats as a proxy for biodiversity. For developments subject to mandatory BNG, the Statutory Biodiversity Metric calculates biodiversity units for area habitats, hedgerows and watercourses. The assessment helps identify habitat losses and gains and determine how the development can achieve the required minimum 10% Biodiversity Net Gain.

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BNG Regulation

HOW DOES THE BNG REGULATION AFFECT YOUR BUSINESS?

Mandatory Biodiversity Net Gain was introduced in England in 2024 under Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. Unless an exemption applies, relevant developments must deliver a minimum 10% increase in biodiversity value. From 2 November 2026, mandatory BNG will also apply to relevant Nationally Significant Infrastructure Projects (NSIPs) in England under a separate BNG framework.

For planning applications made on or after 6 August 2026, updated BNG rules introduced additional exemptions and changes to how the requirements apply.

For applications made on or after 6 August 2026, relevant changes include:

Sites of 0.2 hectares or less: may be exempt, provided onsite priority habitat is not negatively impacted.
Temporary development: may be exempt where the whole development is temporary and permission is for five years or less, subject to the priority-habitat caveat.
De minimis: the existing exemption remains where impacts are below the applicable thresholds, but it cannot be relied upon where priority habitat is negatively impacted.
Self/custom-build: the former exemption has been removed for new applications from 6 August 2026.

Not sure whether BNG applies to your development? Our biodiversity specialists can review your proposed development, site areas and affected habitats to help determine whether an exemption applies and what assessment may be required.

HOW WE CAN HELP

We understand the pressing need to safeguard our natural resources and ensure a sustainable future for generations to come. By adopting responsible practices and embracing cutting-edge solutions, we strive to be at the forefront of biodiversity conservation efforts.

Where mandatory BNG applies, we can carry out a Biodiversity Net Gain Assessment and help develop the Biodiversity Gain Plan and habitat strategy needed to demonstrate delivery of the required minimum 10% net gain.

Where an exemption may apply, we can assess the development against the relevant exemption criteria and provide a supporting report setting out the evidence and justification for review the Local Planning Authority (LPA).

DATA COLLECTION

Our BNG assessment typically begins with a desk-based study, gathering available information about the site, including habitat types, site characteristics and the proposed development or land-use changes. Where further assessment is required and appropriate, a site visit may also be arranged.

This information allows us to establish the baseline biodiversity value of the site and assess how the proposed development may affect habitats and biodiversity units.

CALCULATION

The results identify habitat losses and gains and inform the most appropriate strategy for achieving the required BNG, which may include habitat retention, creation or enhancement onsite and/or registered offsite biodiversity gains. For qualifying minor development submitted from 6 August 2026, the updated biodiversity gain hierarchy allows onsite and offsite options to be considered at the same time, including the option to proceed directly to offsite delivery.

IMPLEMENTATION

Building on the assessment results, we will work with your organisation to develop and appropriate strategy for delivering Biodiversity Net Gain, where applicable. Depending on the development and relevant requirements, this may include onsite habitat creation or enhancement, registered offsite biodiversity gains, or a combination of approaches.

Biodiversity Net Loss

BIODIVERSITY NO NET LOSS & NET GAIN POLICY

Biodiversity No Net Loss is a conservation and environmental policy concept that aims to ensure that the overall level of biodiversity in a particular area remains at least constant, or ideally increases in the case of BNG, after human activities, such as development or infrastructure projects that have taken place.

The goal is to balance any negative impacts on biodiversity caused by these activities with measures that offset or compensate for the losses. The key principles of Biodiversity No Net Loss and Net Gain are:

AVOIDANCE

Avoid or minimise biodiversity loss by planning development projects in a way that has the least impact on natural ecosystems.

MINIMISATION

If biodiversity loss is inevitable, efforts should be made to minimise the impact as much as possible through responsible project design and implementation.

RESTORATION

When biodiversity is lost, there should be a commitment to restore or rehabilitate ecosystems to their pre-development state or improve their condition.

OFFSET

If it is not possible to fully restore the impacted ecosystems on-site, biodiversity offsets come into play. This involves creating or restoring equivalent or an even higher-quality habitat elsewhere to compensate for the loss.

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FREQUENTLY ASKED QUESTIONS

What is Biodiversity Net Gain (BNG)?

BNG is a legal requirement ensuring that development projects leave biodiversity in a better state than before. It aims to increase the quantity, quality, and resilience of habitats.

What is a BNG Assessment?

A BNG assessment evaluates a site’s biodiversity before and after development, using the DEFRA Biodiversity Metric to quantify impacts and determine how much gain is needed.

What does the 10% net gain requirement mean?

Under the Environment Act 2021, most developments in England must achieve at least a 10% net increase in biodiversity compared to pre-development levels, maintained for a minimum of 30 years.

What is BNG regulation? BNG regulation refers to the legal framework mandating biodiversity enhancement for developments. It includes assessment requirements, gain plans, monitoring, and long-term management obligations.

How is a BNG assessment conducted? The process involves:

1. Baseline ecological surveys to map existing biodiversity.
2. Applying the DEFRA Biodiversity Metric to calculate units.
3. Designing a Biodiversity Net Gain Plan with on-site or off-site enhancements.
4. Implementing improvements and establishing long-term monitoring.

How can Tunley Environmental help with BNG assessments? Tunley Environmental provides full BNG services: baseline assessments, metric calculations, net gain plan development, and regulatory compliance support, ensuring projects achieve measurable biodiversity improvements.