BNG: Frequently Asked Questions

BNG is a fast-moving area of policy with a 30-year tail. We’ve grouped the questions we hear most into four themes – what’s changing in 2026, on-site versus off-site delivery, the cost of failure, and how much flexibility the system actually allows. Each answer below is the short version; the linked briefing is the long version.
What changes to BNG are coming in 2026?

On 15 April 2026 Defra confirmed a phased reform package that lands at the end of July 2026. The headline changes are a 0.2 hectare exemption from mandatory BNG covering all development types, withdrawal of the self-build exemption, a new exemption for temporary permissions of up to five years, and a rebalancing of the gain hierarchy so off-site units carry equal preference to on-site delivery on minor schemes. A separate consultation on a targeted brownfield exemption is open until 10 June 2026.

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Download our BNG Reform briefing (May 2026)

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Is my small site exempt from BNG under the new 0.2 hectare rule?
From end-July 2026 (subject to parliamentary scheduling) any development with a red-line boundary at or below 0.2 hectares will be exempt from mandatory BNG, covering all development types — not just residential. There is one important carve-out: the exemption does not apply where priority habitats or irreplaceable habitats are impacted on-site. The current small sites metric continues to apply until the new rules come into force.

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Download our BNG Reform briefing (May 2026)

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Will brownfield sites be exempt from BNG?

Not yet — Defra has not introduced a blanket brownfield exemption. A targeted exemption for residential brownfield development is under consultation, with potential thresholds up to 2.5 hectares, closing on 10 June 2026 and a decision expected later in 2026. In the meantime, the metric definition and condition assessment for Open Mosaic Habitat are being updated to reduce misidentification — worth factoring into current baselines.

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Download our BNG Reform briefing (May 2026)

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Is it better to deliver BNG on-site or off-site?
There is no universal answer — most schemes end up with a blend. On-site delivery is simpler at planning, gives direct control and is visible for ESG, but 30 years of cost and management risk stay with the site. Off-site delivery — either on land you own (“blue-line”) or by buying units from a habitat bank — moves much of that 30-year burden, often at a competitive total cost. The right mix depends on your land, your appetite for long-term management, and your local planning authority.

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How much does BNG actually cost?

It depends entirely on route. Off-site units from third-party habitat banks vary widely — currently £20,000 to £100,000+ per biodiversity unit — but a one-off payment can sit below the cumulative cost of self-delivery, particularly once the 30-year risk is priced in.

What is a habitat bank, and how does buying units work?

A habitat bank is a third-party provider that has already secured land, design, legal agreement and 30-year management for biodiversity units. You reserve units (typically within weeks rather than months) and the provider carries the legal commitments going forward. The trade-offs to weigh: LPAs may want on-site solutions first under the mitigation hierarchy, spatial multipliers apply to units outside your LPA, and provider quality varies — so due diligence on the management plan, ecological credibility and financial security is essential.

 

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What happens if BNG monitoring obligations aren't met?
Less than people fear in the short term, more than people realise in the medium term. The legal architecture is robust but enforcement is currently immature — no BNG-specific criminal prosecutions had been reported as of May 2026, and most LPAs report BNG enforcement is not adequately resourced. The commercial risks, however, are live now: contractual claims for refund and replacement units, reputational damage visible on the public Biodiversity Gain Site Register, financing and insurance impacts, and ultimately regulatory enforcement that is tightening through 2026 and 2027.
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Download our Cost of BNG Failure briefing

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What are the legal penalties for breaching BNG conditions?
The most likely enforcement tool is a Breach of Condition Notice under Section 187A of the Town and Country Planning Act — there is no right of appeal, and non-compliance is a summary offence with a maximum fine of £2,500 per offence, continuing daily. Other tools include Enforcement Notices, Section 106 injunctions for specific performance, and — the nuclear option — Natural England can de-register a Gain Site under reg.15 of SI 2024/45. The crucial point: procedural default (missed reports, missed payments, unreported intervention) is what actually triggers enforcement, not ecological underperformance in itself.
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Download our Cost of BNG Failure briefing

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Who is responsible for BNG monitoring over the 30 years?
It depends on the delivery route. For on-site delivery the responsibility sits with the landowner or management company, secured by Section 106. For off-site delivery on your own land (“blue-line”) it is secured by Conservation Covenant or Section 106 plus entry on the Biodiversity Gain Site Register — and runs with the land. For purchased units, the habitat bank operator carries the 30-year burden. Each year of non-compliance is treated as a fresh breach, so the obligation does not simply lapse.
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Can BNG outcomes or habitat types change after planning?
There is no automatic “as long as units are met” defence in the legislation — the lock-in is procedural, set at four stages: the metric, the Biodiversity Gain Plan, the HMMP, and the Section 106 or covenant. But there are three legitimate doors to flexibility: adaptive management within the agreed targets, periodic re-running of the metric as a diagnostic tool, and — most importantly — a variation clause in the S.106 or covenant that allows the LPA to approve amendments to the HMMP. All three require regulator sign-off; none is automatic.
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Download our Outcome-Led HMMPs discussion paper

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What is an outcome-led HMMP?
An HMMP — Habitat Management and Monitoring Plan — is the document that governs how a BNG habitat is created, managed and monitored over 30 years. An outcome-led HMMP is one written for flexible, trajectory-based delivery rather than fixed-habitat compliance: target conditions set modestly, scenario trajectories annexed, a pre-declared tiered response to underperformance, and plan-revision reviews built in. The principle is straightforward — front-end the flexibility; don’t try to retrofit it.
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What happens if a habitat doesn't reach target condition?
Ecological drift is anticipated and tolerated by regulators — what triggers enforcement is procedural default (silence, missed reports). The expected response to underperformance follows an ISO 9001 plan-do-check-act cycle: a failed report triggers a remediation plan, adaptive management is undertaken and documented, and a re-survey then either demonstrates recovery or escalates the response. The defence is not perfect ecological delivery — it is documented decisions.
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