19th June 2025
Mandatory Biodiversity Net Gain (BNG) has been presenting particular challenges for small developments. When the red line boundary is filled entirely by buildings and/or private gardens, it’s often impossible to achieve 10% gain on-site. Off-site compensation can be difficult to find. This can leave developers and Local Planning Authorities (LPAs) scratching their heads as to how the development can move forward – sometimes resulting in months of back-and-forth.
In fact, there is an existing rule which allows such developments to skip most of the BNG process, simply by paying to compensate for their biodiversity impact:
When a development fills its red line boundary entirely with buildings or private gardens, and needs less than 0.25 Biodiversity Units to achieve 10% BNG, the developer can jump straight to buying statutory biodiversity credits from central government.
This allows smaller developments (potentially up to around 10 residential units, or the equivalent) to avoid any further BNG-related work for the developer or the LPA. Read on to find out how this works, understand what kinds of developments it can be used for, and get practical tips and templates for doing this in practice.
Why is this possible?
- Government guidance states that if a development needs less than 0.25 Biodiversity Units to achieve 10% BNG, the developer does not have to investigate buying off-site BNG compensation from a private provider.
- If the development uses all the on-site land for buildings or private gardens, this straightforwardly demonstrates that it cannot achieve further BNG on-site (beyond the gain delivered by the gardens). No further evidence from the developer is required.
- This means that the developer is automatically permitted to use statutory credits to discharge the biodiversity gain condition, with no further requirements for legal agreements or monitoring of habitats.
How does this work in practice?
This rule makes the BNG process much simpler for both developers and LPAs:
- The developer provides a Biodiversity Metric showing the habitats currently on the site, and their biodiversity value. As a small development, they typically won’t need to engage an ecologist for this work – and digital solutions exist to ease the process.
- The developer’s Biodiversity Metric also needs to show the post-development biodiversity value, but that’s easy: 100% of the land will be buildings or gardens, which are straightforward to enter into the metric based on the site plan.
- The metric’s results can be used to determine the number and type of statutory credits that need to be purchased.
- The LPA only needs to check that (i) the Biodiversity Metric is accurate, and (ii) the developer purchases the correct number of statutory credits. For a small development this can be straightforward, particularly if the LPA uses Verna’s Mycelia software to automate and support the process.
There is no further work for developer or LPA: no legal agreements, no ongoing monitoring or reporting requirements, and no planning conditions (beyond the standard deemed biodiversity gain condition, which will be discharged via the credit purchase).
What size of development does this work for?
Whether a development will require less than 0.25 Biodiversity Units depends on the biodiversity value of the habitats to be affected. If there are highly valuable habitats on the site, the impacts on them may add up to a shortfall of greater than 0.25 Biodiversity Units and this approach may not be available.
For more typical, lower-value initial habitats – such as amenity grassland or cropland – this approach can be used for developments of several houses with gardens, and potentially up to 10 houses or more. (Or an equivalent scale of development, if non-residential.)
For example if you’re building on cropland, and each house has a 100 square metre footprint and a 100 square metre garden, you can create 12 dwellings before breaching the 0.25 Biodiversity Unit limit.
What costs are involved?
If you need to buy the full 0.25 Biodiversity Units’ worth of statutory credits – for example if you’re building 12 houses as in the example above – the cost is likely to be around £21,000 – £24,000. For a smaller development, such as a single house, it’s more likely to be around £1,000 – £2,000.
There may also be cost savings from using this route, for example if it saves the developer ecology consultancy fees, or avoids the need for the developer to pay a BNG monitoring fee to the LPA.
Buying off-site Biodiversity Units from a private provider will typically be cheaper than buying statutory credits from government. As the off-site market is developing, jumping straight to statutory credits gives developers an option to skip the rest of the process and avoid the need to search the market and transact a deal.
How can developers declare to LPAs that they intend to use this option?
You can simply let the LPA know, when you submit your Biodiversity Metric.
For example, you could use the following text. (Feel free to copy and paste this, and to amend it as you see fit.)
As shown in the submitted Biodiversity Metric, the development’s Biodiversity Unit shortfall will be less than 0.25 BUs. The land within the red line boundary will be used entirely for buildings and private gardens, which means that it is not possible to achieve further biodiversity gain on-site. As such, we are planning to discharge the biodiversity gain condition via the purchase of statutory biodiversity credits from Natural England, as permitted under this central government guidance. This means that no further planning conditions, legal agreements, or monitoring arrangements or fees are required. For more information on this approach, please see this article.
How can LPAs let developers know this option is available to help their development proceed?
You can inform the developer at any point. It might make sense to do this early in the planning process, such as during pre-app or validation, to streamline the process from the outset.
For example, you could use the following text. (Feel free to copy and paste this, and to amend it as you see fit.)
Just to make you aware, there may be a straightforward route for this development to meet Biodiversity Net Gain requirements via purchasing statutory biodiversity credits.
Based on your submitted Biodiversity Metric, the development’s Biodiversity Unit shortfall will be less than 0.25 BUs. The land within the red line boundary will be used entirely for buildings and private gardens, which means that it is not possible to achieve further biodiversity gain on-site.
As such, you are permitted to discharge the biodiversity gain condition via the purchase of statutory biodiversity credits from Natural England without providing us with any further evidence. If you take this approach, no further planning conditions, legal agreements, or monitoring arrangements or fees are required.
Government guidance on the use of statutory biodiversity credits is available here, with the option to proceed directly to credits without further evidence set out under “How to prove statutory credits are needed”. For more information on this approach, please see this article.
If you want to use this approach, then when the time comes to purchase statutory credits you can do so here. Please ensure that you purchase the exact numbers and types of credits required, based on the Biodiversity Unit shortfalls shown in the finalised Biodiversity Metric for the development.
Spread the word!
This option has been in place since the start of mandatory BNG, and could address many frustrations, but it is little known. Wider awareness could save time, cost, and confusion for developers and LPAs. Please feel free to share this article.
If you have any questions or feedback on this, you can reach out to us on mycelia@verna.earth.