Biodiversity Net Gain

What is Biodiversity Net Gain?

Biodiversity Net Gain (BNG) is an approach to development and land management that aims to leave the natural environment in a measurably better state than it was before. Schedule 7A of the Town and Country Planning Act 1990 makes it mandatory for all non-exempt developments requiring planning permission to demonstrate a 10% net gain in biodiversity.

Introduced as part of the Environment Act 2021 with a series of new legal requirements, BNG is intended to contribute to tackling the nature crisis currently underway in the UK. As detailed in the State of Nature Report 2023, the UK is now one of the most nature-depleted countries on Earth. In the context of Surrey, the State of Surrey’s Nature Report estimates that 1 in 9 species native to the county are now locally extinct. By mandating developments to demonstrate measurable net-gains for biodiversity, BNG creates a legal requirement for habitat creation and enhancement. The result is intended to contribute to ‘bigger, better, more joined up’ habitats in line with the Making Space for Nature Lawton Review 2010 and the creation of a resilient ecological network that will allow species to recover.

State of Nature 2023 - report on the UK’s current biodiversity

The Surrey Context

This webpage is intended to supplement the nationally published resources for Biodiversity Net Gain (BNG) and is not an exhaustive outline of the statutory method. The information included here sets the context for the requirements of Biodiversity Net Gain in planning applications to Surrey County Planning Authority. All applicants are strongly advised to reference and have regard to the published documents on the Government website when preparing documents to submit for planning.

How is BNG measured?

BNG uses the Statutory Biodiversity Metric Calculation Tool to quantify the value of a site’s habitats using ‘units’ that reflect their relative ecological importance. By comparing the unit values of a site’s existing baseline habitats with its proposed post-development habitats, the net change in value can be calculated. BNG can be achieved by improving and/or creating habitats on site, off site, or as a last resort via the purchase of statutory credits. Applicants can use a combination of all three to achieve the minimum threshold of 10%. For a full outline of the method and the rules which must be complied with for statutory BNG, applicants should refer to the Statutory Biodiversity Metric User Guide on the Government website.

Surrey County Council requires a minimum 10% Biodiversity Net Gain consistent with the national statutory minimum. However, applicants should be aware that this can vary across the Districts and Boroughs within Surrey, who may have specific policies within their Local Plans, requiring a higher percentage of BNG to be achieved. If an application falls within a Local Authority area, where a higher percentage net gain target is required by a Development Plan policy this will need to be met within the application. Links to the Surrey District and Borough policy pages can be found on the Development plans webpage.

Statutory Requirements

To comply with the statutory requirements of BNG, there are several key documents which applicants and their ecologists should have reference to. These documents contain the ‘musts’, (legal requirements) of BNG. Anything within an application that contravenes or deviates from a ‘must’ would be non-compliant with the law and therefore not valid for use in determining planning applications/discharging conditions.

For up-to-date information on BNG, it is always recommended that applicants consult the official Government website

Statutory Biodiversity Metric calculation tool (SBM): This is the excel spreadsheet that uses pre-set values and the results of ecological site surveys to calculate the habitat unit values. The SBM itself is a statutory instrument and no other calculation tools can be used or submitted with planning applications. The Small Sites Metric (SSM) is also available for use on smaller application sites.

BNG User Guide: This is the comprehensive technical manual that accompanies the SBM (with a separate document for the SSM). It outlines in detail how data should be collected and how the spreadsheet should be used. It contains many of the statutory rules for BNG, compliance with the user guide is mandatory.

Biodiversity Gain Hierarchy: The Biodiversity Gain Hierarchy is a material consideration for Local planning authority (LPA). How an application has followed the hierarchy will be scrutinised on review of both application documents and the Biodiversity Gain Plan. This hierarchy (which does not apply to irreplaceable habitats) sets out a list of priority actions:

Avoid impacts to onsite habitats which have a medium, high and very high distinctiveness.
If it is shown that avoidance is not possible, impacts to such habitats should be mitigated,
Finally, where impacts cannot be avoided or mitigated, impacts should be compensated for in prioritising in order, where possible, via the enhancement of existing onsite habitats, creation of new onsite habitats, allocation of registered offsite gains and finally the purchase of statutory biodiversity credits.

What to submit with a Planning Application

The Government sets out clear minimum requirements for what information an applicant must provide when submitting a planning application. If this information is not submitted, the LPA should refuse to validate the application. The minimum requirements are found within the Biodiversity net gain: what local planning authorities should do government webpage.

Surrey County Council's Local List for the Validation of planning applications can be found on the Local List for the validation of planning applications. Each Annex of the Local List sets out the information requirements expected to be submitted with each application type. Applicants should be aware that the statutory minimum requirements for information are limited, and whilst the final BNG calculations are intended to be submitted with the Biodiversity Gain Plan, the County Planning Authority needs be a confident when determining the application that the biodiversity gain condition is capable of being discharged and the biodiversity gains can be delivered.

Additional information may therefore be requested at the planning application stage where there is uncertainty over the capability of the biodiversity gain condition being successfully discharged. The primary reasoning for this could be:

To have confidence that the Biodiversity Gain Plan will be capable of being successfully discharged post-consent;
To sufficiently inform any legal agreements or planning obligations that may be required to secure BNG (see on-site significant enhancements);
To streamline the discharge of the pre-commencement BNG condition;

To discharge the pre-commencement condition the applicant will have to demonstrate that any off-site gains have been legally secured, either by evidencing the habitat bank on the national register, or by providing a copy of the bespoke s106 or conservation covenant entered into for the purposes of BNG. If the applicant is purchasing statutory credits, evidence of this purchase will need to be submitted to discharge the pre-commencement condition.

Pre-application advice: BNG is new, nuanced and site specific. We strongly encourage applicants to engage with the County Council’s pre-application planning advice service to discuss any BNG queries ahead of making a planning application.
Pre-application discussions for planning applications - Surrey County Council

Exemptions

Some types of planning application are exempt from BNG, these are outlined in full detail on the Government website for biodiversity net gain and exempt developments.

One example of exempt developments are applications which fall below the threshold for BNG and qualify under the de minimis exemption. Such applications do not impact priority habitat and:

Impact less than 25m² of on-site habitat
Impact less than 5 metres of on-site linear habitats (such as hedgerows and lines of trees)

If applicants wish to use the de minimis exemption, they must submit a supporting justification statement which evidences that their scheme will fall below the threshold. This ideally should be completed by an appropriately qualified person. There are several factors to consider and evidence when asserting that a planning application falls below the statutory BNG threshold such as:

Impact: An impact to a habitat is defined as any direct loss of habitat, but also any indirect degradation / reduction in that habitats condition as a result of development. For example, some good condition grassland may be retained within a development site, however the proposed use of the site/changes in hydrology would result in this habitat deteriorating over time. This would constitute an impact and would disqualify an application from being de minimis if over 25m² of habitat was affected in this way.

Edge effects: An additional consideration when determining if a habitat is impacted or not. For example, a woodland that borders a field proposed for re-development for an extension to a school site. How will the habitat be affected? Are additional measures to control access required to protect the current condition of the habitat?

Watercourses: A watercourse is considered impacted if development occurs within its riparian zone, defined as a set distance from the bank top of the watercourse. In the Statutory Biodiversity Metric User Guide this rule applies to rivers, streams, canals (a 10m riparian zone) and ditches (a 5m riparian zone). If greater than 5m of such habitat is affected, statutory BNG is then required.

Loss of individual trees.

Individual trees are represented spatially in the SBM as area-based habitats measured in hectares. A small tree of poor condition equates to 0.0041ha of habitat, which equals to 41m². This exceeds the minimum threshold of 25m², therefore, if an application is losing an individual tree it will not qualify under the de minimis exemption.

Significant on-site enhancements

Significant on-site enhancements are defined as ‘areas of habitat enhancement which contribute significantly to the proposed development’s BNG, relative to the biodiversity value before development’. The creation and maintenance of these significant enhancements must be secured with a legal agreement (planning obligation or conservation covenant) or planning condition for 30 years. The most appropriate mechanism to secure BNG will be agreed during the determination of the planning application.

The Government list of what may count as significant is outlined here on their website and listed below Make on-site biodiversity gains as a developer. What counts as a significant enhancement will vary depending on the scale of development and existing habitat, but these would normally be:

habitats of medium or higher distinctiveness in the biodiversity metric
habitats of low distinctiveness which create a large number of biodiversity units relative to the biodiversity value of the site before development
habitat creation or enhancement where distinctiveness is increased relative to the distinctiveness of the habitat before development
areas of habitat creation or enhancement which are significant in area relative to the size of the development
enhancements to habitat condition, for example from poor or moderate to good

Reporting significant on-site enhancements

Applicants are encouraged to provide their own assessment as to whether they think any of their proposed habitats would qualify as significant. Any significant on-site gains require additional monitoring measures to ensure their successful delivery. Negotiating this could be a key part of determining an application (for example if a Section 106 agreement is required). We therefore encourage early discussion with the County Planning Authority to establish a clear expectation of any monitoring requirements Pre-application discussions for planning applications - Surrey County Council

Strategic Significance

Strategic significance is one of the mandatory habitat quality multipliers applied within the statutory biodiversity metric calculation tool. For a full outline of all the multipliers, applicants should refer to the Statutory Biodiversity Metric User Guide on the Government website.

The strategic significance multiplier provides a ‘boost’ to the unit value of habitats where they are identified as being locally important for nature conservation. It is divided into three categories: high, medium and low. This multiplier is linked closely with the Local Nature Recovery Strategy (LNRS) and different rules apply before and after the LNRS is published (please see tables 7 and 8 in the Statutory User Guide).

Pre-LNRS:

For applications submitted to Surrey County Council before publication of the LNRS, the documents to use when determining the strategic significance multiplier are the objectives and targets documents for Surrey’s Biodiversity Opportunity Areas (BOAs). Surrey has 50 individual BOAs that are grouped into their respective National Character Areas (NCAs). BOAs ‘represent a targeted, strategic approach to conserving and enhancing biodiversity, and form the spatial basis for planning Surrey’s ecological network.’ BOAs comprise a combination of designated sites for nature conservation and also undesignated areas containing priority habitat types (as listed under Section 41 of the Natural Environment and Rural Communities Act 2006). For further detail on BOAs, please see the BOA Policy Statements published by Surrey Nature Partnership .

Pre-publication of the LNRS, the strategic significance multiplier should be applied as follows:

You should apply the High strategic significance category to habitats in the baseline sheets if your site is within a BOA and the habitat type is specified within that BOAs restoration / creation targets.
You can apply the High strategic significance category to habitats in the post-intervention sheets if your site is within a BOA and the created or enhanced habitats are those specified within the BOAs restoration / creation targets

Where the definition for high strategic significant is not met, low strategic significance must be applied. The medium strategic significance multiplier can only be applied when the LPA has not identified a suitable document for assessing strategic significance.

Post-LNRS

Once Surrey’s LNRS is published, it will become the deciding document in determining where in the county can be referenced as ‘high’ strategic significance for nature conservation. Any sites located outside of the LNRS can only be referenced as ‘low’ strategic significance. The ‘medium’ strategic significance category is no longer applicable post publication of the LNRS. The Local Nature Recovery Strategy webpage provides updates on the Surrey LNRS.