On 12th February 2024, BNG will become mandatory for all major planning applications in England, although this has been a long time coming for many within the industry as the Environment Act, which enforces the requirement by law, received Royal Assent in November 2021.

Essentially this piece of legislation mandates BNG in the planning process, making it a requirement for all appropriate developments to deliver a minimum 10% net gain in biodiversity. As such, the Environment Act 2021 amends the Town & Country Planning Act (TCPA) and 2008 Planning Act (NSIPs). Please note that BNG for minor development comes into force from 2nd April 2024 and for NSIPs it will become mandatory from November 2025.

The forthcoming BNG legislation does not replace or diminish any current protection for biodiversity or the processes that are currently required i.e. ecological impact assessment, arboricultural survey, flood risk assessment etc.

It is also important to remind our clients that BNG is essentially a pre-commencement requirement and therefore exact details – other than confirming that the mandatory 10% net gain will be achieved – do not need to be provided upfront to Local Planning Authorities (LPAs), although it is anticipated that many LPAs will request this information prior to the application being submitted.

However, the LPA decide to act, it is imperative for developers to consider BNG early on in the site analysis and design process to ensure that a sufficient net gain can be achieved. Here, the collaboration of Ecologists, Landscape Architects and the wider consultant team is crucial.

The BNG habitats associated with new development proposals must be secured and managed for at least 30 years, with the responsibilities set out in a legal agreement. It is important to note that if applicable, the 30 years of BNG management and maintenance starts from the time the agreed initial habitat creation or enhancement is completed (for example, after one year of tree planting, pond digging or seeding).

BNG Metric

BNG is calculated through a mandatory biodiversity metric that measures the baseline, or the existing habitat and features on a site prior to any development proposals taking place and provides a baseline biodiversity unit value for the site. A second calculation is then undertaken to measure the post development biodiversity unit value. Ultimately, the difference between the two calculations is the biodiversity net gain or loss.

A developer must confirm a minimum of 10% net gain in biodiversity against the baseline, whether these new habitats are created on-site, off-site or a combination of both (more on this later).

The metric used is currently at version 4.0, with earlier editions including 2.0 in 2019, 3.0 in 2021 and 3.1 in 2022. The metric is essentially a habitat-based approach to determine a proxy biodiversity value. In order to streamline the process of inputting survey data (biodiversity value) into the metric, Phase 1 Habitat Surveys or Preliminary Ecological Appraisals (PEAs) have been replaced by UK Habitats Classification surveys.


What is a Biodiversity Unit?

Biodiversity units are a proxy to describe biodiversity and include the following:

  • Area Units
  • Hedgerow Units
  • Watercourse Units

As outlined above, BNG applies to each habitat type that is present when the baseline score is measured.

For example, a site with 100 area units, 20 hedgerow units and 40 watercourse units will need to provide as a minimum, post-intervention (or post development) units of: 110 area units, 22 hedgerow units and 44 watercourse units.


On-site or Off-site? How to deliver BNG

Developers should be looking to retain and protect any aspects of high ecological value as the loss of these habitats will ultimately make it harder to achieve a net gain, especially if the habitats are of a rarer value.

Once the baseline score has been established, the developer can choose to provide habitat creation and enhancement within the site, with the landscaping and green infrastructure considered by the design team – here Landscape Architects and Ecologists can assist to ensure the scheme is carefully planned for placemaking, people and biodiversity with net gain being delivered through ‘on-site units’ if this is achievable.

Alternatively, the developer may choose to provide their BNG through ‘off-site units’ through the creation of habitats or enhancement on adjacent land owned by the same developer i.e. blue land, or within their wider land holdings. Off-site units can also be purchased from habitat banks, which may be from the Environment Bank, Land Trust, Wildlife Trusts etc or the open market through private landowners and land agents. For example, Savills (use their ‘Environmental Exchange’, a map based database designed to connect those parties who require offsets with those able to provide them), Fisher German etc or local planning authorities as well.

It is important to note that developers can utilise a combination of both off-site and on-site units in order to achieve the mandatory 10% BNG. Critically, developers must be clear whether the BNG is being delivered on-site, off-site or a mixture of the two from the outset, as this will be taken into consideration for the planning judgement by the decision makers. Developers should also be aware that if BNG is generated off-site, it ideally needs to stay ‘local’ i.e. within the same National Character Area (NCA) as the monetary value of habitat units (purchased from habitat banks i.e. Environment Bank or private landowners) to fulfil BNG requirements increases the further they are created from the application site.

Landowners are now making the most of the emerging natural capital market by looking at transitioning from agricultural and arable uses to facilitate habitat banks to sell on the open market to developers looking to achieve BNG in the local and wider area.

The last option for developers (and the most expensive) is to purchase ‘Statutory Credits’, this is the least preferred option and therefore should only be used if on-site and off-site units are not available. These credits refer to landscape scale, strategic habitat creation delivering nature-based solutions.


As outlined earlier in this briefing, developers should be looking to do the following;

  • Avoid – retain, protect and enhance,
  • Mitigation – recreate and enhance ‘On-Site’, or
  • Compensate – create and enhance ‘Off-Site’.

The metric is weighted towards compensation being the last resort and therefore this is the least cost-effective way for developers to comply with BNG legislation. However, it should also be emphasised that achieving BNG on-site is not always possible or preferable for the long-term conservation of such habitats, especially as features created through BNG must be managed for at least 30 years.


Key Summary

  • Retain the most valuable habitats i.e. those rarer habitats or those that take longer to establish (woodland and wetland) or watercourse units, which often cannot be replicated;
  • Integrate non-developable land i.e. steeper areas or areas liable to flooding so that BNG can be created on-site;
  • Habitats that score high within the metric are wildflower meadows and native landscapes that are species rich or have pockets of woodland and include scrub;
  • BNG habitats should link to Local Nature Recovery Strategies;
  • BNG should provide benefits to local communities through access to green space and nature as well as the social and wellbeing benefits this simultaneously delivers, especially in urban areas;
  • BNG enhancements should be considered within the context of other local landscape and ecology policies such as community woodlands to ensure the enhancements are well suited to the landscape character of the site and its surroundings;
  • Don’t forget Green Infrastructure, landscaping, public open space, SuDS can all contribute to the BNG score and can therefore be multi-purpose features within a planning application; and
  • The statutory credits trading scheme is a last resort option and is a scheme managed by Natural England to deliver rarer and harder to create habitats. There is no direct link between the impacts project and compensation site.


Implications for Planning Decisions 

At a headline level, the BNG legislative will result in the imposition by default of a planning condition on a grant of permission requiring the submission and approval of a Biodiversity Gain Plan (BGP), prior to the commencement of the development approved.

Even if not expressly imposed or stated on a decision notice by a Local Planning Authority, amendments to Section 56 of the TCPA, will ensure that such a condition is deemed to be imposed in a similar manner to those regarding the normal statutory time periods controlling the life span of permissions.

As part of a suite of related legislative amendments, there will no requirement for the applicant to agree to such a pre-commencement condition, with the ability to amend it via a Section 73 or Section 96A Non-Material Amendment applications also removed. In addition, in confirming the status and importance of achieving BNG, the ability to seek ‘Deemed Discharge’ of an application for the approval of a BNG via Articles 28/29 of the Town and Country Planning (Development Management Procedure (England) Order 2015 (as amended) (‘the Procedure Order) has also been disapplied.


However, not all planning applications would be subject to the new BNG condition, with the following types generally exempted:

  • Householder Applications;
  • Self-Build or Custom proposals than fall within the Procedure Order definition of a minor scheme;
  • Applications for Biodiversity Gain Sites;

There is also a ‘’De Minimis’ exemption for schemes where there is no loss of a priority habitat and the on-site habitat effected falls within defined limits (circa 25m2). Works carried in accordance with Development Orders would also be exempt, thereby including those undertaken as permitted development.


Transitional Arrangements and Section 73 Applications 

In recognition of the existence of many live applications within the planning system, the requirements for mandatory BNG and the associated BGP condition are subject to transitional arrangements.

In the case of major applications, the requirement for BGP conditions does not apply for applications made prior to the 12th February 2024.

For minor application, the requirement does not apply for applications made prior to the 2nd April 2024.

Hence for live applications already in the system or for those made before these dates, the BGP condition will not apply. It is however highlighted that whilst the legislation does not provide a clear definition as to ‘made’, this would normally be taken to be applications which were valid prior to the key dates.


In terms of Section 73 applications, the requirement does not apply where:

  • the original planning permission to which the section 73 planning permission relates was granted before 12th February 2024; or
  • the application for the original planning permission to which the section 73 planning permission relates was made before 12th February 2024.

It should be noted however that the ‘original planning permission’ is taken to be first planning permission granted i.e. the baseline one. If this original permission has been the subject of one or more earlier Section 73 decisions and the new Section 73 application relates to one of these latter decisions rather than the original one, the requirement for BNG may need to be met.

Thinking ahead to Section 73 applications made in respect of decisions which will be already subject to a BGP condition and where a BGP has been approved, if the amendments applied for do not alter the approved BGP, then the approved BGP will carry forward. However, if the reverse is true, fresh consideration of BNG will be required and an appropriate further approval of a BGP. It is therefore essential that full consideration as to the implications on BNG, of any post determination amendments are fully considered ahead of submission.


Compliance with the Biodiversity Gain Plan Condition 

The need to apply for the approval of pre-commencement planning conditions is a long-established principle and one that all developers are familiar with. Indeed, most if not all major / minor schemes require the submission and approval of details such as materials, landscaping schemes and drainage plans, all of which are normally considered by the LPA and their consultees.

With regard to a scheme for a Biodiversity Gain Plan, it can be seen that the delivery of biodiversity net gain can be done in a number of ways as set out in the Biodiversity Gain Hierarchy. Where gains are to be delivered on site, this should be a straightforward process for the developer to do and in turn a straightforward condition submission. Although thought will need to be given as to how the onsite gains can be secured for the relevant 30-year period, especially if the land / scheme is to be sold on.

However, where the gains are to be delivered by way of purchasing units off site or in a worst case scenario in a National Scheme, matters will become more complicated.

In such cases, the BGP condition submission will need to include full details of where the units are being delivered as well as when and how their delivery will be secured. This approach will involve the purchase of units which may in turn require the completion of legal agreements with the appropriate BNG scheme landowners, all of which will take time to prepare and collate for a submission.

Given that the BGP condition has a prior to commencement trigger and will be seen as being of a ‘condition precedent’ nature, early consideration of how to discharge the condition will be required.

It would be highly unwise to leave the submission of a BGP condition discharge application to the last minute, particularly in case of projects where the objective is merely to implement a permission rather its completion.


Going forward into 2024…

Pegasus Group will continue to assess BNG across the various development sectors as it is formally implemented into the planning system. A draft biodiversity net gain planning practice guidance was published by Department for Levelling Up, Housing and Communities in November 2023 and it is expected that this will be updated in due course. Our teams will carefully monitor the latest guidance and ensure we provide further advice as appropriate so we can keep all our clients up to date.



James Sutton james.Sutton@pegasusgroup.co.uk

Darryl Rogers darryl.rogers@pegasusgroup.co.uk

Robyn Friesner robyn.friesner@pegasusgroup.co.uk