B
Biodiversity Gain Plan
A document required for each non-exempt development, demonstrating how the 10% BNG uplift will be achieved. Must be approved by the LPA before development can lawfully commence. Includes the metric calculation, on-site habitat proposals, off-site allocations, and any statutory credit purchases.
Biodiversity Net Gain (BNG)
The mandatory planning requirement in England for most new developments to deliver at least a 10% measurable improvement in biodiversity value compared to the pre-development baseline. Introduced under the Environment Act 2021 and mandatory since February 2024.
See: What is BNG?
Biodiversity Unit
The standard unit of measurement for biodiversity value, calculated using the Statutory Biodiversity Metric. Based on habitat area (or length), type, distinctiveness, condition, and other factors. There are three types: area habitat units, hedgerow units, and watercourse units — these are not interchangeable.
Broad Habitat Type
A general habitat classification used in the biodiversity metric — for example, "grassland", "woodland", or "wetland". Each broad type contains multiple specific habitat types. The trading rules require losses to be compensated within the same broad habitat category where possible.
See: Trading rules
C
Condition
The ecological quality of a habitat, assessed as Good (score 3), Moderate (score 2), or Poor (score 1). Condition is one of the key inputs to the biodiversity metric and is assessed by an ecologist during the baseline survey using DEFRA's condition assessment criteria.
Conservation Covenant
A legally binding private agreement between a landowner and a designated responsible body to conserve the natural or heritage features of the land. For BNG, covenants must run for at least 30 years. Created under Part 7 of the Environment Act 2021, available since September 2022, and registered as local land charges that bind future landowners.
See: Legal agreements
D
Development Consent Order (DCO)
The consent mechanism for Nationally Significant Infrastructure Projects under the Planning Act 2008. From May 2026, DCO applications must demonstrate 10% BNG. The Secretary of State is the decision maker, not the LPA.
See: NSIPs
Difficulty Multiplier
A factor in the biodiversity metric reflecting how difficult it is to create or restore a given habitat type. Ranges from 1.0 (straightforward) down to 0.1 (very difficult). Only applies to proposed/created habitats, not baseline. Each habitat type has a fixed difficulty score in the DEFRA lookup tables.
Distinctiveness
A measure of a habitat's ecological rarity and importance, assigned by DEFRA to each habitat type. Graded as Very High (score 8), High (6), Medium (4), Low (2), or Very Low (0). Distinctiveness determines the trading tier, which controls what habitat can compensate for what.
E
Environment Act 2021
The primary legislation establishing mandatory BNG in England. Received Royal Assent in November 2021. Amends the Town and Country Planning Act 1990 (via Schedule 7A) to require 10% biodiversity net gain as a planning condition. Also introduced conservation covenants (Part 7) and provisions for extending BNG to NSIPs.
See: What is BNG?
Exemption
A development type that is not required to deliver BNG. Current exemptions include sites impacting less than 25 sqm of habitat (rising to 0.2 hectares in late 2026), householder applications, and permitted development. A targeted brownfield exemption for sites up to 2.5 hectares is also under consultation.
See: Exemptions · Exemption Checker tool
G
Gain Sites Register
The national public register maintained by Natural England listing all registered off-site BNG habitat bank sites in England. Sites must be legally secured (via conservation covenant or S106) before they can be registered. Developers' off-site unit allocations are also recorded on the register.
H
Habitat Bank
A site where habitats are created or enhanced specifically to generate biodiversity units for sale to developers. Habitat banks must be legally secured for 30 years and registered on the national Gain Sites Register before units can be sold. As of early 2026, there are 197 registered gain sites covering approximately 7,000 hectares.
See: Landowner guide
Habitat Management and Monitoring Plan (HMMP)
A practical document setting out exactly how BNG habitats will be created, managed, and monitored over the 30-year obligation period. Agreed between the landowner and the responsible body or LPA. Includes target conditions, management prescriptions, monitoring schedules, trigger points, and financial provisions.
See: Legal agreements
I
Irreplaceable Habitat
Habitats such as ancient woodland, blanket bog, and limestone pavement that cannot be offset through standard BNG trading or statutory credits. Development resulting in loss of irreplaceable habitat requires bespoke compensation and may be refused under NPPF paragraph 186(c) unless "wholly exceptional reasons" exist.
See: Trading rules
L
Local Nature Recovery Strategy (LNRS)
Statutory strategies required under the Environment Act 2021, identifying priorities and locations for nature recovery in each area of England. LNRSs influence the strategic significance multiplier in the biodiversity metric — habitats aligned with LNRS priorities score higher. Over half have been adopted, with the remainder expected in 2026.
See: 2026 reforms
Local Planning Authority (LPA)
The local council responsible for planning decisions in a geographic area. For BNG, LPAs assess planning applications, approve Biodiversity Gain Plans, confirm statutory credit eligibility, and monitor long-term compliance. There are 309 LPAs in England, of which only 107 currently have registered habitat banks.
See: LPA guide
M
Mitigation Hierarchy
The mandatory order in which developers must deliver BNG: first on-site (within the development boundary), then off-site (purchasing units from habitat banks), then statutory credits (buying from the government as a last resort). Each step must be exhausted before moving to the next.
N
National Character Area (NCA)
One of 159 geographic areas in England defined by Natural England based on landscape character, geology, and ecology. The BNG metric uses NCAs for geographic matching of off-site units — units from the same NCA as the development are preferred over those from adjacent or more distant NCAs.
See: Trading rules
Nationally Significant Infrastructure Project (NSIP)
Major infrastructure projects (energy, transport, water, waste) consented via Development Consent Orders under the Planning Act 2008. BNG becomes mandatory for NSIPs from May 2026, requiring a minimum 10% uplift secured for 30 years.
See: NSIPs
O
Off-site Biodiversity Gain
Habitat creation or enhancement delivered on land outside the development site boundary, used when the full 10% BNG cannot be achieved on-site. Off-site gains must come from sites registered on the national Gain Sites Register and be secured for at least 30 years. The second priority in the mitigation hierarchy.
Open Mosaic Habitat
A habitat type found on previously developed (brownfield) land, characterised by a mix of bare ground, early successional vegetation, and varied micro-habitats. Classified as Medium distinctiveness in the metric, which has proven controversial because it requires like-for-like offsetting even on apparently derelict sites. The definition is under review as part of the 2026 reforms.
See: 2026 reforms · Exemptions
R
Responsible Body
An organisation designated by DEFRA to enter into conservation covenant agreements with landowners. Responsible bodies monitor compliance, enforce breaches, and submit annual returns to DEFRA. Must be a public body, charity, or other organisation with conservation-related main purposes or activities. Current designated bodies include Wildlife Trusts, RSK Wilding, and various LPAs.
S
Section 106 Agreement
A planning obligation under Section 106 of the Town and Country Planning Act 1990, used to secure BNG delivery. An agreement between the developer/landowner and the LPA, registered as a local land charge. Used for both on-site significant habitat gains and off-site BNG. The established alternative to conservation covenants.
See: Legal agreements
Small Sites Metric
A simplified version of the full Statutory Biodiversity Metric, designed for use on smaller development sites. Reduces the data input requirements and complexity of the calculation while maintaining the same core methodology.
Spatial Risk Multiplier (SRM)
A multiplier applied to off-site biodiversity gains to account for the ecological risk of compensating at a distance from the development site. For statutory credits, the SRM is a fixed 2x — meaning developers must purchase two credits for every one unit of shortfall. For private market units, the SRM varies and is built into the metric calculation.
See: Statutory credits · Trading rules
Statutory Biodiversity Credit
A credit purchased from the government (via Natural England on behalf of DEFRA) as a last resort when on-site and off-site BNG delivery are not possible. Priced at a deliberate premium starting at £42,000 per credit, with a 2x spatial risk multiplier making the effective cost £84,000+ per unit. Revenue funds national habitat creation projects. Non-refundable.
Statutory Biodiversity Metric 4.0
The mandatory DEFRA calculation tool for measuring pre-development and post-development biodiversity value in standardised units. Published November 2023. Uses habitat area/length, distinctiveness, condition, strategic significance, difficulty, and temporal multipliers to produce biodiversity unit values. Distributed as an Excel spreadsheet (.xlsm).
Strategic Significance
A multiplier in the biodiversity metric reflecting whether a habitat is located in an area identified as a priority for nature recovery — typically linked to Local Nature Recovery Strategies. High significance = 1.15x, Medium = 1.10x, Low = 1.00x (no bonus).
T
Temporal Multiplier
A discounting factor in the biodiversity metric that accounts for the time it takes a newly created habitat to reach its target condition. Habitats that mature quickly (3 years) receive little discount; those taking 30+ years are heavily discounted (down to ~0.33x). Only applies to proposed/created habitats, not baseline.
Trading Rules
Rules within the biodiversity metric ensuring that habitat losses are offset by equivalent or higher quality habitat types. The core rule is "like-for-like or better" — you can trade up (replace low distinctiveness with high) but never down. Geographic preferences also apply: same LPA is preferred, then same NCA, then adjacent NCA. Hedgerow and watercourse units cannot be substituted with area units.
See: Trading rules
Trading Tier
A classification derived from a habitat's distinctiveness score that determines what can offset its loss. Five area tiers (A1–A5) plus separate hedgerow (H) and watercourse (W) tiers. A5 (Very High) requires bespoke compensation; A4–A2 require same-tier-or-better; A1 (Very Low) can be offset by any tier.
See: Trading rules
V
Very High Distinctiveness
The highest distinctiveness tier (A5, score 8), covering habitats like ancient woodland, blanket bog, lowland raised bog, and limestone pavement. These habitats are effectively irreplaceable and cannot be offset through standard trading or statutory credits. Any development impacting Very High habitats requires bespoke compensation agreed with the LPA.
See: Trading rules