Mandatory BNG went live for all planning applications from 2nd April 2024. We have been talking to planners in the PAS BNG Network to find out how they are handling the first applications. We are turning what we are learning into a set of live topics and will update them each week as we build up a bank of knowledge. The information contained here is produced by Planning Advisory Service (PAS). It does not represent offical Government policy or guidance.
There has been a few differences in how councils are viewing whether BNG should apply from the application date or the validation date. Most councils are choosing to be pragmatic and choosing NOT to apply the BNG condition where a planning application is:
- received before the BNG live date(s), failed validation, and then made valid after the BNG live date(s).
- validated before the BNG live date(s), was later found to have errors, and re-validated after the BNG live date(s).
- received via the portal over the early April 2024 Bank Holiday weekend.
Competency for the Small Sites Metric is site specific. Can the person using the SSM confidently identify habitats present at baseline? Do they know the management requirements for retained, enhanced and created habitats on-site?
The Local Planning Authority (LPA) has a role to assess the information provided in the statutory biodiversity metric calculation tool but is not expected to assess the competency of the person who supplied it.
LPAs should trust that the person supplying the habitat information has followed the Small Sites Metric (SSM) User Guide and satisfied themselves that they are competent. If the LPA is in any doubt about the competency of the person providing the information, it may request a ‘competency statement’ to support this. In this statement the LPA may ask the user to set out what training, qualifications, or experience they have. Competency should not be used as a reason to ignore the advice of an ecologist where it may be justifiably required / given.
An example definition
Here is an example definition of competency contained in an LPA’s guidance that PAS finds useful:
(The Council) recommend the metric assessment be completed by a competent person as follows:
• Biodiversity Metric Assessment - A suitably qualified ecologist who has achieved Field Identification Skills Certificate (FISC) of Level 3 or above or holds a CIEEM accreditation. Evidence will need to be provided showing the required qualifications of the appointed Ecological consultant.
• Small Sites Metric Assessment – A person capable in identifying habitats present on the site before the development and identifying the management requirements for habitats which will be created or enhanced within the landscape design. The competent person must carry out the habitat survey and assessment and be able to confidently identify the habitats likely to occur in a given geographic location at the time of year the survey is undertaken.
You must be a qualified assessor to undertake a river condition assessment.
Self-Build/ Custom-Build proposals are exempt from the mandatory BNG condition. There are some specific challenges that Self-Build/ Custom-Build applications are presenting:
- How to determine if an application is a genuine Self-Build/ Custom-Build proposal?
- What happens to the BNG requirement if the development is proven not to be Self-Build/ Custom-Build after planning consent is granted?
- Can an approach be taken that is similar to Community Infrastructure Levy (CIL) where a ‘disqualifying event’ triggers the CIL requirement?.
- Is there some way of connecting the BNG requirement to the consent for a Self-Build/ Custom-Build development via a condition or a legal agreement?
- If a ‘breach’ occurs, there is the question of the ‘penalty’. Perhaps National credits for the "lost" units could be applied or taking a similar approach to where ‘degradation’ has occured?
- There won’t be a baseline metric (as these proposals are exempt). Should LPAs do their own pre-development assessment to record a baseline?
- It seems sensible to try and be consistent with pre-existing ways of securing self-build (and CIL exemptions).
Right To Build Task Force: How to prove self - and custom-build?
We like some of the thinking from the right to build taskforce. Pre-BNG they were already trying to tie the requirements of a custom/self build into the decision via an obligation. Right To Build Task Force have lots of useful info defining self and custom build with a useful definitions guide including a 'separating custom and self-build from speculative house building' section.
What else is being done?
DLUHC is strengthening the definitions for the Self-Build/ Custom-Build register requirments and will be consulting on options soon for what the definition might mean including the use of conditions, Unilateral Undertakings, and s106. There is a keeness to have a standard approach across all LPAs. Model templates will follow and theree may be different mechanisms between small plots and a % of self-build on a large site*.
* Note only exclusively self-build developments are exempt from BNG.
DLUHC has published suggested text for use on decision notices to help local planning authorities to comply with the requirements on Biodiversity Net Gain. The use of this suggested text is discretionary, and local planning authorities should make decisions on the content of their decisions notices and may wish to get their own legal advice.You can find a link to the suggested text in paragraphs 025 and 026 of the Biodiversity Net Gain PPG.
What is degradation?
The degradation of habitats refers to activities carried out that lower the biodiversity value of habitats prior to a planning application being made on a site that includes those degraded habitats. Local Planning Authorities (LPA) will want to establish the biodiversity value of habitats on any given site prior to the degradation (the pre-development biodiversity value) - so that the correct biodiversity baseline can be established, and the correct biodiversity gain is secured once the planning application has been approved.
The Environment Act 2021
To address concerns over the potential for the wilful degradation of habitats (e.g. to reduce the baseline biodiversity value of a development site and reduce the cost of achieving a 10% Biodiversity Net Gain), the Environment Act 2021 stated that if unauthorised activity (i.e. not in accordance with a planning permission) that degraded habitats that has taken place on or after 30 Jan 2020, then the pre-development biodiversity value of that onsite habitat is taken to be the biodiversity value of the habitats immediately before the carrying on of the activities that lowered the biodiversity value.
The Levelling Up and Regeneration Act 2023 (LURA)
In 2023, the Levelling Up and Regeneration Act 2023 (LURA), introduced additional wording further tightening of the law regarding degradation by extending the circumstances in which degradation can be addressed. This wording stated that any authorised activity (i.e. in accordance with a planning permission) that is carried out on onsite habitats, or any unauthorised activity (i.e. not in accordance with a planning permission) that is carried out on offsite habitats on or after the 25th August 2023, that cause the biodiversity value of the habitat to be lower than it would otherwise have been on the relevant date (usually the date that a planning application is made), then the pre-development biodiversity value of that habitat is taken to be its biodiversity value immediately before the carrying on of the activities that degraded/lowered the habitat’s biodiversity value.
BNG Planning Practice Guidance (PPG) Feb 2024
The PPG refers to both dates for on-site habitat, but does not mention the 25th August 2023 in respect of offsite habitats.
Scenarios
These scenarios are to illustrate how to apply the Legislation dates (effectively the 'backstop' dates) and the dates LPAs should be measuring the degradation from.
- Onsite degradation - NOT in accordance with a planning permission:
Where activities are carried out on land that lower the biodiversity value of onsite habitat and are carried out not in accordance with a planning permission between 30th January 2020 and the relevant date (usually the planning application date), then the pre-development biodiversity value of that onsite habitat is to be taken to be its biodiversity value immediately before the carrying on of the activities that lowered the biodiversity value. .
- Onsite degradation IN accordance with a planning permission (other than the new planning application currently being considered):
Where activities are carried out on land that lower the biodiversity value of onsite habitat and are carried out in accordance with a planning permission (other than the new planning application currently under consideration) between 25th August 2023 and the relevant date (usually the planning application date) of the new planning application currently under consideration, and development for which that other planning permission was granted:
- has not been begun, or
- has been begun but has not been completed
then the pre-development biodiversity value of the onsite habitat of the new planning application currently under consideration is to be taken to be its biodiversity value immediately before the carrying on of the activities that lowered the biodiversity value.
- Offsite – degradation NOT IN accordance with a planning permission.
Where activities are carried out on land that lower the biodiversity value of offsite habitat and are carried out not in accordance with a planning permission between 25th August 2023 and the relevant date (usually the planning application date), then the pre-development biodiversity value of that offsite habitat is to be taken to be its biodiversity value immediately before the carrying on of the activities that lowered the biodiversity value.
Legislation Dates - Quick Reference Guide:

The De Minimis exemption is designed to account for the very smallest or least impact planning applications. The De Minimis exemption is set out in Regulation 4 of the Biodiversity Gain Requirements (Exemptions) Regulations 2024. It is narrowly defined to exclude very specific types of development - such as accessibility ramps and telecommunications masts.
Key points to consider:
- Evidence should be provided to justify the use of the de minimis exemption. This is set out in the Planning Guidance: "When providing reasons for the de minimis exemption, an applicant should provide sufficient evidence... where the development would be smaller than 25 square metres, the description of development, existing and proposed site plans, and the development’s area size (in square metres) may be sufficient evidence. In other cases where it cannot be clearly demonstrated through site plans and descriptions whether an onsite habitat would be lost or degraded by the development, applicants are strongly encouraged to provide a completed metric for the pre-development and post-development value for the onsite habitat and clear plans identifying the nature and size of this pre-development onsite habitat and how much of it will be impacted by the development.
- Trees (see separate section below) - the removal of one small tree is normally enough to disqualify a development from the De Minimis exemption (this is to do with the root protection area and canopy). A small tree >7.5cm (diameter at breast height (dbh) has an area habitat of 41 square metres, therefore if one small tree is impacted on-site, the de minimis exemption cannot be claimed.
- The fact that land is not being built on doesn't automatically mean that habitats on this within the site boundary won't be impacted or affected by building elsewhere on the site - tree roots for example may be affected by a development.
- The biodiversity gain planning condition does not apply in relation to planning permission for development which meets the first and second condition.
- The first condition is that the development does not impact an onsite priority habitat.
- The second condition is that the development impacts less than 25 square metres of onsite habitat that has biodiversity value greater than zero; and less than 5 metres in length of onsite linear habitat.
- Please note, that habitat can still be impacted if not completely lost due to development. Potential impacts to habitat conditions can comprise types of disturbance such as footfall, lighting etc. and should be considered when reviewing de-minimis claims.
In England, all planning permissions are generally subject to biodiversity gain rules. However, some permissions are specifically exempt. BNG was introduced as a general condition for planning permission - as set out in the Environment Act 2021: "grants of planning permission in England [are] to be subject to a condition to secure that the biodiversity gain objective is met".
It is early days for BNG - we are all learning - and there is the potential for exemptions to be mistakenly claimed by applicants and accepted (by Local Planning Authorities (LPAs)) - it is worth looking at the sections on 'De Minimis', and 'Custom/Self Build' on this page as these are topical.
Care should be taken to advise applicants correctly about the circumstances and types of applications that are currently exempt from mandatory BNG, and ensure that the correct evidence is always provided to support applications that are claiming the exemption.
Claiming exemption from BNG
If an applicant claims that their application is exempt from the mandatory Biodiversity Net Gain (BNG) requirement, the Local Planning Authority (LPA) should consider whether the proposal is genuinely exempt at the validation stage. Early evidence suggest that there is a fair degree of uncertainty on which exemptions apply, in what circumstances and when.
LPAs will want to consider particularly carefully those applications claiming the De Minimis exemption - it is not just the size of the site/habiats affected but also has to account for impact, distinctiveness and type (see also the section below on Trees) of habitat.
Applicants should set out what exemption(s) apply to the development and where appropriate provide evidence in a report of some kind (for example, where it cannot be clearly demonstrated through site plans and descriptions). Photos are a useful source of evidence and some councils are using drones where parts of a site have limited access.
Where a submitted post-development Statutory Metric contains trading rule errors, would this prevent validation of the application, or is this an issue that should be subject to discussion between validation and determination?
The options:
It's best to try to keep things as simple as possible at validation stage, however there is a balance. Anything beyond obvious mistakes such as not actually meeting 10% where they have also submitted the post-development metric, may require looking at more closely. A nuanced approach / site-by-site consideration should be taken, including:.
- As the national validation list doesn't ask for submission of a post-development metric, the application could be validated.
- Your local validation rules may require some form of indication as to the post development metric, so:
- The metric will need to be revised prior to determining the application.
- For large / complex / high distinctiveness, you may wish to request that the errors are corrected before validating the application.
- The trading rule error could be because the development is proposing to use off-site units and the details haven’t been sorted out yet.
You may request that the applicant provide very obvious and logical information to explain any such reasons why the statutory metric rules have not been met.
DLUHC are bringing BNG for retrospective permissions as the second part of the implementation of BNG. Retrospective permissions require a slightly different framework because a pre-commencement condition cannot be applied as the development has already been commenced. This is why retrospective permissions have been listed as exempt for the time being. DLUHC are working through this as it will require further regulations. The second part of BNG implementation will also include the extension to BNG to other routes to permission such as Local Development Orders (LDOs).
Schedule 7A Para 9 (b) of the TCPA 1990 (as updated by Schedule 14 of the Environment Act 2021) states that 'significant' is based on what the planning authority considers is significant in relation to the pre-development biodiversity value. This is why it is relative to the site (pre-development biodiversity value) and the LPA can determine what they consider significant.
The guidance states that 'significant enhancement' varies depending on the scale of development and existing habitat, but it will normally involve:
- habitats of medium or higher distinctiveness,
- habitats of low distinctiveness that create a large number of biodiversity units relative to the biodiversity value of the site before development, and
- areas of habitat creation/enhancement that are large relative to the size of the development.
"Significant" doesn't necessarily mean 'a great amount'. It is relevant to the site. You may not be able to make a judgement about significance until post consent. Note also that retained habitat can't be significant (only enhanced habitat).
Examples in the guidance
The guidance uses a wildflower meadow or a nature park as examples of what could count as a significant enhancement on a development site which is providing a significant increase in biodiversity units in relation to the baseline and would need to be secured by planning condition, section 106 agreement or conservation covenant for 30 years.
The guidance also contains examples of non-significant enhancement e.g. a private gardens which have a low distinctiveness value, or container planting. These enhancements do not normally require maintenance provisions, so for non-significant enhancements, you do not need to have an HMMP, legal agreement or commitment to maintain them for 30 years.
How LPAs are approaching this
While we are all still getting used to things, many LPAs are taking a cautious approach and where there is doubt, putting the onus on the applicant to be clear and explain why the enhancement proposed on a development site isn't significant.
LPAs are able to determine their own definition of significant enhancement/BNG. For example, in Leeds City, on-site BNG is considered significant where the combined total Biodiversity Units (BUs) for area habitats, hedgerows and watercourses is 5 or more.
The statutory metric guidance states that: The biodiversity metric uses set values to represent the area of individual trees depending on their diameter at breast height. This value is a representation of canopy biomass, and is based on the root protection area formula, derived from BS 5837:2012. Many applicants have not realised the removal of a tree on a development site will mean the application is not exempt under the de-minimis exemption. When assessing trees as part of the biodiversity baseline, it is the root protection area and the canopy that are considered.
Example: The ‘tree helper’ in the statutory biodiversity metric calculation tool, calculates that that 1 small tree in poor condition = 41 square metres (the de-minimis threshold is 25 square metres). So, if this tree is removed the development will not be exempt.
The Biodiversity Metric Principle (2) states that the metric does not override existing biodiversity protections, statutory obligations, policy requirements, ecological mitigation hierarchy or any other requirements. Principle (6) also highlights that the metric is designed to inform decisions in conjunction with locally relevant evidence, expert input, or guidance.
The retention of existing trees should be prioritised at the earliest possible stage to minimise potential impacts. This includes all tree-related habitats, such as groups, lines, blocks, or individual trees. When planning to retain trees, it is essential to thoroughly review all survey findings, including the condition assessments that support the metric. This review is crucial for verifying and confirming the accuracy of the data entered into the associated metric.
Trees classified as 'ancient' or 'veteran' will be appropriately documented in the relevant ecological report and condition assessment. If such habitats are identified on-site, they must be included in the metric calculation, selecting the option that identifies them as irreplaceable habitats.
Development should avoid the loss or deterioration of these habitats unless there are exceptional circumstances and a suitable compensation strategy is in place. Since the assessment of impacts and suitable compensation for irreplaceable habitats falls outside the BNG process, they are excluded from the baseline calculation. Compensation for any impacts must be agreed upon separately with the LPA.
Typically, habitats within private gardens are not assessed separately for BNG purposes but are recorded as either ‘vegetated’ or ‘unvegetated’ gardens. However, for trees, any garden tree with a trunk diameter of 30 cm or more (measured 150 cm from the ground) must be included in the metric baseline, regardless of Tree Preservation Orders. This ensures the biodiversity value of any significant garden trees is properly accounted for in the baseline and encourages their retention.

There is a lot of useful debate about what information (on top of the statutory minimum) that could / or should be asked for at validation stage. The debate is around what to ask for as a local list, and are there 'minimum' and 'optional' versions of this?
It really is one of those things that is up to each LPA and needs to be factored against the type, scale and nature of the development and the BNG requirement.
The jury is out on whether there could or should be a ‘definitive’ list – PAS view is that this needs to be decided locally and will adapt/change with experience. The ‘what can we insist on?’ question is understandable, but also difficult to be definitive on. LPAs need to set sensible, proportionate and justifiable local validation requirements and take an appropriate stance where these are not met - can the information be provided later or is it so fundamental that the application can't be validated?.
Here are some useful examples of validation requirements provided by our BNG network:
- Chelmsford local validation requirements
- Newcastle draft validation checklist 2024
- Northumberland's Northumberland CC's draft local list requirements: BNG Local Validation Requirements - _Biodiversity net gain forum for LPAs
See also - 'Evidence to support exemptions'.
The Statutory Biodiversity Metric User Guide states that when accounting for temporary losses, you do not need to record a habitat as lost when there are temporary impacts to a habitat and the area can be restored to both baseline habitat type and baseline condition within 2 years of the initial impact.
Please note it may be considered good practice if the party/ies responsible for completing the metric outline a temporary loss within the comment’s column of the relevant tab for the reviewer.
These habitats may also be entered as ‘enhanced’ if the action is proposed to enhance the habitat above its original habitat type and condition. If this is the case, it is advised that a 1 or 2 year delay be applied to the starting habitat type within the creation and/or enhancement tab.
If local, regional policies or permissions are already in place for requirements regarding specific baselines, then accounting for temporary impacts cannot be applied to the metric.
When referring to the metric, the User Guide states that strategic significance derives from the local significance of the habitat based on its location and the habitat type. It is discussed further within the guide, that each individual habitat parcel is to be assessed separately both at baseline and at post-intervention, for on-site and off-site.
Parcels are only to be split if they are intersected by a boundary between two areas of different strategic significance and/or a planning authority boundary. For any off-site habitats, it is advised that strategic significance is assessed using local policy documents relevant to the offsite location and not the development location.
If a Local Nature Recovery Strategy (LNRS) has been published, then it is advised that this document is used in alignment with the table shown below.

If there is no existing LNRS, it is advised that alternative local policy documents are to be used in conjunction with Table 8 shown below. If no alternative local policy documents exist, then medium strategic significance can be applied if the criteria within Table 8 are met. Some examples of ‘alternative policy documents’ comprise local neighbourhood plans, BAP’s, river basin management plans, green infrastructure strategies and many more. Further examples of suitable policies that can be used for assessing significance can be found within the User Guide.

- Prior to the publication of a draft LNRS, LPA’s should publicly communicate which strategy or plan is to be used to determine the strategic significance multiplier in the metric for baseline and post development habitats.
- Publicly communicate proposed LNRS consultation draft and publication dates so applicants are prepared for any metric reassessments of the strategic significance multiplier for live applications or for discharge of the pre-commencement condition.
- Pre-development baseline values submitted prior to the published LNRS should remain unchanged,
- If the LNRS is published during a live application or prior to discharge of the pre-commencement condition, then the initial post-development baseline value is to be updated.
- If a LNRS has already been published, then for new, non-exempt, applications submitted following publication must:
- Mark the SS multiplier as ‘Low’ for all on and off-site habitats.
- Mark the SS multiplier as ‘High’ for habitats that meet the criteria within Table 7, page 28 of the user guide (habitats are to be marked low if they do not meet the criteria).
- The ‘Medium’ multiplier category is not to be used if there is a published LNRS.
Good Practice examples from Local Planning Authorities:
General BNG Guidance for applicants:
Validation:
- Chelmsford local validation requirments
- Newcastle draft validation checklist 2024
- Northumberland BNG Local Validation Requirements - _Biodiversity net gain forum for LPAs
Habitat Bank Applications: