Biodiversity gain plan: what it means in planning
The biodiversity gain plan is a separate approval from planning permission. This explains what it contains, when it must be submitted, and which schemes are exempt.
A biodiversity gain plan is the document a developer submits to the council, after permission is granted and before development starts, showing how the scheme will deliver at least a 10 per cent uplift in biodiversity value. The council has to approve it. Until it does, development cannot lawfully begin.
It comes from the Environment Act 2021, which inserted a new schedule into the Town and Country Planning Act 1990 and attached a biodiversity gain condition to most planning permissions in England automatically, whether or not the decision notice mentions it.
What the plan contains
The plan is a factual document rather than an argument. It sets out the pre-development biodiversity value of the site, measured with the statutory metric, along with the post-development value the scheme will achieve.
Value is expressed in biodiversity units, calculated from habitat type, size, condition, distinctiveness and location. The idea is explained more fully in biodiversity units explained, and the condition element of the calculation, which is the part most often disputed, in habitat condition assessment in a biodiversity metric.
The plan also states how the uplift is made up. On-site habitat creation and enhancement come first. Registered off-site gains, either on land the developer controls or purchased from a habitat bank, come next. Statutory biodiversity credits bought from government are the last resort and are priced to be so.
Finally, it identifies any irreplaceable habitat, which sits outside the ordinary metric arrangements and is dealt with separately.
Where it comes from in law
The Environment Act 2021 created the regime, and the biodiversity gain condition is deemed to be imposed on permissions granted under Part 3 of the 1990 Act, subject to exceptions.
Duties arrived in two stages. Major development came into the regime on 12 February 2024. Small sites followed on 2 April 2024. Nationally significant infrastructure projects were brought in later on their own timetable.
The statutory metric is published by government and updated periodically, and the version used has to match the one current when the calculation was made. Version control is a real issue on schemes with long lead times, and it is covered in downloading the biodiversity metric and version control.
The gain has to be maintained for at least 30 years, secured by a planning condition, a planning obligation or a conservation covenant, with the monitoring and management arrangements set out.
How councils apply it
The plan is submitted to the local planning authority, which must decide whether to approve it. This is not a discretionary planning judgement in the way determining an application is. The authority checks that the metric has been completed correctly, that the habitats and their condition have been recorded properly, and that the gain is secured.
Refusal is possible, and there is a right of appeal against it. In practice most plans that fail do so because the pre-development baseline is wrong, because the condition assessment cannot be supported by the survey evidence, or because the off-site units have not actually been registered.
Councils also check the date of the baseline. The pre-development value is normally taken at the date of the application, which stops a developer from clearing a site and then claiming a low starting value. Where habitat has been degraded since 30 January 2020, the authority can require the earlier value to be used.
An illustrative example
Take a field of modest grassland proposed for 20 homes. Survey work records the grassland, a hedgerow along one boundary and a small group of trees.
The metric calculates a pre-development figure in habitat units and hedgerow units, which are counted separately. The proposed layout retains the hedgerow, plants a new one, creates a wildflower meadow along the site edge and adds garden and amenity planting. That gets the scheme most of the way but leaves a shortfall in habitat units, because gardens score poorly and the meadow takes years to reach good condition.
The shortfall is met by purchasing off-site units from a registered site in the same national character area, which avoids the spatial risk penalty applied to units bought further away.
This example is illustrative. Real calculations depend on the habitat types recorded, their condition, the metric version and the trading rules.
Where it is commonly misunderstood
The most frequent error is treating the plan as part of the planning application. It is not. It comes afterwards, and preparing it late is one of the most common causes of delay between permission and starting on site.
The second is assuming that a landscape plan delivers the gain. Landscape drawings and metric calculations are prepared for different purposes, and a scheme designed without the metric in mind usually falls short. Run the calculation at design stage, not after.
The third is thinking that 10 per cent means 10 per cent more trees. It is a measure of habitat units, in which condition and distinctiveness matter more than quantity, and a small area of high quality habitat can outweigh a large area of amenity grass.
The fourth is assuming that delivering net gain answers any other ecological requirement. It does not touch protected species licensing, and it is unrelated to the tests under the habitats regulations.
Exemptions and terms that sit nearby
Some development falls outside the regime, including householder applications, certain self-build and custom build schemes, development below a small de minimis threshold of on-site habitat, and development on a registered biodiversity gain site itself. The detail of what is caught and when is set out in biodiversity net gain start dates and transitional rules.
A local nature recovery strategy is a separate document that identifies where habitat creation would do most good, and off-site units in a priority area can score better. It is worth reading before choosing where to buy units.
What to do if it applies to your site
Commission the ecological baseline survey early, in the right season, because the metric depends on habitat condition assessed on the ground rather than from a desk.
Then run the metric at concept design stage and see what the layout does to the number. Ask the ecologist for the calculation in the metric spreadsheet rather than as a summary paragraph, because the assumptions sit in the cells and not in the prose.
And ask the council early whether it has a local policy going beyond the statutory 10 per cent. Some authorities have adopted higher targets through their local plans, and a scheme designed to the national minimum then has to find the difference late. Moving a road or keeping a hedgerow costs little on a drawing and a great deal after permission.
A Biodiversity Net Gain Assessment has to be prepared by a competent person under the Environment Act 2021 regime, and the local planning authority approves the gain plan itself. An AI-assisted draft is a starting point for that professional rather than a substitute for them.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required. This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. Enter your postcode on PlanScope to see which ecology documents a site is likely to need.
Frequently asked questions
When does the biodiversity gain plan have to be submitted?
After planning permission is granted and before development begins. The biodiversity gain condition is deemed to be attached to most permissions in England, and development cannot lawfully start until the local planning authority has approved the plan. Preparing it late is a common cause of delay between permission and work starting on site.
Who approves the plan?
The local planning authority. Its role is to check that the statutory metric has been completed correctly, that habitats and their condition are properly recorded, and that the gain is secured for at least 30 years. There is a right of appeal against a refusal to approve a submitted plan.
Which developments are exempt?
Householder applications, certain self-build and custom build schemes, development affecting only a very small area of on-site habitat, and development on a registered biodiversity gain site are among the exceptions. The boundaries of these exemptions have shifted since the regime started, so check the current guidance rather than relying on an older summary.
Does the 10 per cent apply to trees or to area?
Neither directly. It applies to biodiversity units calculated by the statutory metric, which combine habitat type, size, condition, distinctiveness and location. Hedgerows and watercourses are counted separately from area habitats. A small area of high quality habitat can carry more units than a much larger area of amenity grassland.
Can I clear the site before applying to lower the baseline?
No. The pre-development value is normally taken at the date of the application, and where habitat has been degraded since 30 January 2020 the authority can require the earlier, higher value to be used instead. Clearance before application is treated as reducing the baseline artificially and is dealt with accordingly.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.