Change to Timeline for 10% Biodiversity Net Gain becoming mandatory


Government has set out next steps on plans for new housing, commercial and infrastructure developments to be “nature positive” by confirming that upcoming legislation to bring in these rules will be laid in November 2023.

Under the updated timetable set out 27 September 2023 developers in England will be required to deliver 10% “Biodiversity Net Gain” from January 2024 onwards when building new housing, industrial or commercial developments meaning by law they must deliver a net positive for the local environment, for example by creating new habitats and green spaces.

Biodiversity Net Gain for small sites will be applicable from April 2024, and implementation for Nationally Significant Infrastructure Projects is planned for 2025.


  • Developments over 1 ha or 9 units – 10%  BNG mandatory January 2024 (Major Developments)
  • Developments under 1 ha and no more than 9 units – 10%  BNG mandatory April 2024
  • Nationally Significant Infrastructure Projects -10%  BNG mandatory  is planned for 2025

IMPORTANT: the requirement for BNG when it becomes mandatory only applies to new applications, it will not apply to applications pending in the planning system.

On 29th November 2023, the Government published all guidance and the regulations including:


Biodiversity net gain (BNG) is a strategy to develop land and contribute to the recovery of the environment. It is a way of making sure the habitat for wildlife is in a better state than it was before development.

Our Practical Guide to Biodiveristy Net Gain covers the basics of BNG, and our blog Biodiversity Net Gain: UK Government Introduces New Measures may also be useful to readers.

Biodiversity Net Gain is an important step towards reversing the decline in biodiversity, but its requirements present challenges for developers. Let us share some insights into the options and how to prepare.

Under the Environment Act, development needs to achieve a minimum 10% gain in biodiversity.  Under previous plans from November 2023, all development submitted for planning permission must submit details demonstrating how lost habitat will be replaced, plus 10% extra, this is known as Biodiversity Net gain (BNG). This can be done onsite or through biodiversity offsetting elsewhere.

Onsite solutions involve dedicating land for habitat restoration within the development site. There are a few key risks for developers who opt for onsite biodiversity net gain solutions:

  • Long-term management responsibilities – Developers take on the legal obligation to maintain, monitor and report on habitat condition for 30 years after project completion. This exposes them to risks over decades.
  • Temporary setbacks become permanent failures – A fire, disease, or random event wiping out newly created habitats onsite could lead to irreplaceable losses triggering non-compliance.
  • Difficulty meeting obligations on dense urban sites – Space constraints in built-up areas may limit meaningful onsite mitigation, increasing the challenges of delivering the required 10% gain. This is particularly challenging for smaller scale developments.
  • Cost overruns from habitat establishment – Unexpectedly high costs of establishing new natural spaces like wetlands or meadows could impact project finances and timelines.
  • Ongoing access issues for monitoring/maintenance – Habitats fragmented across residential plots introduce access and permission difficulties for long-term upkeep duties.
  • Reputational risk from habitat degradation – Developers remain accountable if habitats decline over 30 years, risking damage to their brand from non-compliance issues.
  • Assumption of unforeseen management complexity – The intricacies of maintaining diverse ecoystems may expose developers to demands beyond their core competencies.

In many cases, onsite biodiversity net gain poses long-term risks developers may prefer to transfer (offset) the risk and responsibilities to projects specialising in land management.

Offsetting transfers responsibility offsite to another piece of land in the local area. Large-scale habitat banks are restoring hundreds of hectares across the country. These establish diverse landscapes like woodlands and wetlands to provide offsetting units for developments.

Purchasing units from established banks offers several benefits. Developers avoid long-term management duties. Costs remain reasonable by using inexpensive agricultural land. And habitat linking enhances the landscape’s resilience.

Understanding local requirements and identifying who can provide the needed offsetting units and which projects are available to ‘buy’ into brings certainty.

Buying into a Council project or through a Biodiversity Bank can be a simple solution.  However there are opportunities to offset BNG to land within the local area without going through a third party, however this could come with risks similar to that of providing onsite BNG.

With two ecosystems in recovery – development and the natural world – offsetting through habitat banking provides a constructive solution respecting both. Developers need to start conversations now to hit the ground running when the regulations take full effect.  Whilst it is acknowledged that BNG has been set in planning policy in some Councils for a while now, the November 2023 BNG requirements make it mandatory.

BNG credits are a core component of how biodiversity net gain is measured and delivered through offsetting projects.

Here’s a quick overview of what BNG credits are:

  • Metrics: BNG credits are calculated using the Defra biodiversity metric, which assesses the biodiversity value of habitats based on factors like size, condition and rarity.
  • Units: One credit (or unit) represents the biodiversity value of a hectare of land that has been enhanced to provide a distinct habitat or ecosystem.
  • Requirements: Developers must purchase enough credits to offset the biodiversity loss from their project and achieve the mandatory 10% net gain.
  • Generation: Credits are generated through conservation projects that restore or create new priority habitats over large areas, like habitat banking schemes.
  • Banking: Credits from approved offsetting projects are registered, monitored and held in a ‘biodiversity bank’ available for purchase by developers.
  • Purchasing: Developers can buy pre-existing credits from approved banks to meet their mitigation and net gain obligations.
  • Condition: Credits remain attached to the land and its management in perpetuity to ensure the biodiversity benefits are secured long-term.

In essence, BNG credits provide the standardised currency that allows biodiversity losses and gains to be measured, mitigated and traded to deliver the net benefits required under the new environmental regulations.

Buying statutory biodiversity credits is considered by the Government as a last resort option for developers if you are unable to use onsite or offsite units to deliver BNG.  Statutory biodiversity credit prices have been released in July 2023, however these are indicative but could help developers plan ahead.

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Planning House work with some brilliant Ecologists and other consultants who could assist you in preparing your BNG plans for your development project, feel free to CONTACT US.

BNG November 2023