Mandatory biodiversity net gain (BNG) has been in force in England since February 2024. If planning permission for your spring scheme was granted on or after 12 February 2024 for a major development, or on or after 2 April 2024 for a small site, the project has a legal obligation to deliver BNG before work can start. That means a biodiversity gain plan must be submitted to and approved by the local planning authority (LPA). You cannot mobilise without it.

Winter is the time to sort this out. Spring programme commitments have a way of landing before the ecology is arranged, and by then the room to manoeuvre has narrowed considerably.

The 10% uplift and what it is measured against

BNG requires the biodiversity value of a site after development to be at least 10% higher than it was before. That value is calculated in biodiversity units using the Statutory Biodiversity Metric, a tool developed by Natural England. The metric scores each habitat by type, condition, area and strategic significance. Bare earth and short amenity grass score low. Species-rich grassland in good condition scores considerably higher.

The starting figure comes from the baseline survey. A qualified ecologist visits the site, records the habitats present and enters the data into the metric to produce a biodiversity unit total. The developer then models the post-development picture. If the 10% target is not met by on-site measures alone, the shortfall has to come from somewhere else.

Why the survey has to happen before clearance

This is the detail that catches contractors out. If site clearance happens before the ecologist has carried out the baseline survey, the habitats that were there are gone before anyone has recorded them. The metric needs data from the actual site as it stands. LPAs have flagged cases where pre-commencement clearance removed habitats the gain plan was supposed to account for, stalling the scheme in the process.

There is also a timing issue with protected species. Nesting bird surveys broadly apply from March to August, and surveys for great crested newts and dormice need to happen at specific times of year. If any of these are required on your scheme and have not yet been arranged, a March start may push you into the breeding season before the assessments are complete.

How the shortfall gets covered

Where on-site habitat creation cannot deliver the full 10%, the developer has two options. The first is to purchase biodiversity units from a registered habitat bank, a landowner who has committed land to habitat management for at least 30 years. The second is to buy statutory biodiversity credits directly from Natural England. These are priced substantially higher than habitat bank units, intentionally, because the policy intent is to make genuine habitat creation the more attractive route.

The checks to run before mobilisation

Before work starts, confirm these with the developer or their agent:

  • Has the biodiversity gain plan been approved by the LPA? Approval is a pre-commencement condition. No approval, no start.
  • Does the plan identify features that must be retained during construction? Hedgerows, ponds and veteran trees often appear as protected elements with specific avoidance requirements.
  • Are any protected species surveys still outstanding? Ask the ecologist directly, not just the programme planner.
  • Is there a habitat management plan covering the 30-year post-construction period? Someone needs to be named as responsible for it before works begin.

Treating the biodiversity gain plan like a ground investigation report makes this easier: commission it before the programme is committed, not the week you need to start. The earlier the ecologist goes in, the less likely survey findings are to force a programme change.

Did you know? Under the Environment Act 2021, biodiversity gain plans must secure habitat management for at least 30 years. This applies whether the gain is delivered on-site or through off-site units purchased from a registered habitat bank, not just for the construction period.

Frequently asked questions

Does BNG apply to a project with planning permission granted before February 2024?

Mandatory BNG does not apply to consents granted before 12 February 2024 for major developments, or before 2 April 2024 for small sites. However, some LPAs have encouraged voluntary BNG on earlier schemes, so it is worth checking any planning conditions carefully.

Can we start site clearance before the ecological baseline survey?

No. The baseline survey must be completed before any clearance or ground disturbance. Once habitats are removed, they cannot be assessed retrospectively, and the gain plan calculation loses its foundation. LPAs may require the completed baseline before pre-commencement conditions are discharged.

What if we cannot hit the 10% uplift on site?

The shortfall can be covered off-site by purchasing biodiversity units from a registered habitat bank, or by buying statutory biodiversity credits from Natural England. Credits are priced substantially higher by design, so habitat bank units tend to be the more practical route where they are available.

Who produces the biodiversity gain plan?

The developer, or their planning consultant or ecologist, is responsible for producing and submitting the biodiversity gain plan. It must be approved by the local planning authority before any works can start. The contractor's role is to implement what the plan specifies on site.

How long do on-site BNG habitats need to be managed?

Under the Environment Act 2021, habitat management must continue for a minimum of 30 years after the gain condition is granted. This long-term commitment applies to both on-site habitats and off-site units secured through habitat banks.