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Blue Harbour Estates | Blog 16 | Published 1 September 2026 TL;DR: the short answer Under mandatory Biodiversity Net Gain (BNG) in England, the landowner is legally responsible for creating or enhancing the habitat and then managing it for at least 30 years to reach a defined target condition. That responsibility is locked in by …
Blue Harbour Estates | Blog 16 | Published 1 September 2026
Under mandatory Biodiversity Net Gain (BNG) in England, the landowner is legally responsible for creating or enhancing the habitat and then managing it for at least 30 years to reach a defined target condition. That responsibility is locked in by a planning condition, a Section 106 agreement or a conservation covenant, and it does not expire when the developer leaves site.
In practice, almost no landowner does that work themselves. They appoint a grounds maintenance contractor to deliver the Habitat Management and Monitoring Plan (HMMP) year after year, record what was done, and feed evidence back to the local planning authority. BNG is written by ecologists, approved by planners, and then delivered by grounds teams for three decades.
If your site has a BNG obligation attached to it, the practical question is not “how do we get planning permission” any more. It is “who is cutting that wildflower meadow at the right time of year in 2041, and can they prove it.”
BNG is an approach to development that leaves habitats for wildlife in a measurably better state than they were beforehand. It became mandatory in England under Schedule 7A of the Town and Country Planning Act 1990, inserted by Schedule 14 of the Environment Act 2021.
The headline number is 10 per cent. Unless the development is exempt, it must deliver at least a 10 per cent uplift in biodiversity value, measured in standardised biodiversity units using the statutory biodiversity metric. Units are affected by habitat size, quality, location and type.
There are three ways to deliver it, and developers are expected to work through them in order:
The bit everyone underestimates is what happens next. For off-site gains and significant on-site gains, the habitat must be maintained for a minimum of 30 years, starting from when the development is complete.
Thirty years. That is roughly ten grounds maintenance contract cycles.
Two things moved this year, and both are worth knowing before you assume you are off the hook.
From 6 August 2026, developments with a red line area of 0.2 hectares (2,000 square metres) or below are exempt from mandatory BNG. Government analysis suggested this single change would exempt roughly half of the residential planning permissions that previously needed to comply. Read the carve-out carefully though: the exemption does not apply where the development negatively affects on-site priority habitat. The previous self-build and custom build exemption was withdrawn as part of the same package, and a new exemption was added for temporary development permitted for five years or less.
Also from 6 August 2026, the on-site-first hierarchy applies only to major development. Minor developments that are not otherwise exempt can now weigh on-site and off-site delivery at the same time, and can go straight to off-site if that suits them better.
And from 2 November 2026, BNG applies to Nationally Significant Infrastructure Projects, under a separate set of rules.
Here is the point that gets missed. None of this touches obligations already granted. If your site received permission in 2024, 2025 or the first half of 2026 with a BNG condition attached, that 30-year clock is still running. The new exemptions apply to new applications, not retrospectively to commitments already secured through a legal agreement.
So the practical takeaway for commercial property in Kent is simple. Fewer new sites will pick up a BNG obligation. But a large and growing stock of sites already carry one, and every year that passes adds more of them to the pile that needs managing.
The land owner. GOV.UK is unusually direct on this point: the land owner is legally responsible for creating or enhancing habitat, and managing that habitat for at least 30 years to achieve the target condition.
That applies whether you are making on-site gains or selling off-site gains on land you own. If you have bought off-site units instead, you are paying a land manager to carry that same burden on your behalf.
Where it gets interesting for commercial property is the definition of “land manager” in the government’s own guidance. It explicitly includes facilities, property and estate managers, land agents, estate owners and planning authorities using their own land. If you run a business park, a distribution centre, a school estate, a care campus or a housing association portfolio, that is you.
And responsibility does not transfer when the site is sold. A conservation covenant or a Section 106 obligation runs with the land. Buy a commercial site with a BNG obligation and you have bought the maintenance liability along with the car park.
In almost every case, a grounds maintenance contractor. The chain looks like this:
| Role | Who typically holds it | What they do |
|---|---|---|
| Legal responsibility | Landowner / freeholder | Carries the 30-year obligation, faces enforcement |
| Design and metric | Ecologist | Baseline survey, metric calculation, writes the HMMP |
| Approval and oversight | Local planning authority | Approves the biodiversity gain plan, receives monitoring reports |
| Year-by-year delivery | Grounds maintenance contractor | Cuts, plants, weeds, replaces failures, records evidence |
| Independent monitoring | Ecologist, periodically | Condition assessments against metric criteria |
The contractor is the only party on that list who is physically on the site more than once a year. Which means the quality of your BNG outcome is, in practice, decided by whoever holds your grounds maintenance contract.
The HMMP is the document that turns an ecologist’s promise into a maintenance schedule. It sets out how the habitat will be managed, monitored and reported on across the full 30-year period.
A workable HMMP should give your contractor:
Worth knowing: management and monitoring obligations are mandatory for all off-site gains, but on site they bite only where the enhancement is classed as significant. Non-significant on-site enhancements do not require an HMMP, a legal agreement or a 30-year commitment. So the first question on any site is which of your habitat areas are actually caught.
Where monitoring does apply, the outcomes must be reported to the LPA. There is no fixed national interval. The HMMP sets out when and how habitats will be monitored and results reported, and that schedule is agreed with the LPA or responsible body based on the habitats involved and how complex the site is. Natural England’s HMMP template offers an indicative schedule, but check what your specific agreement says rather than assuming a standard interval.
If your HMMP is vague, your contractor will default to conventional amenity maintenance, and conventional amenity maintenance is exactly what destroys biodiversity units.
This is the part worth reading twice, because it is where most sites lose their units.
A well-run traditional grounds maintenance regime is built around neatness and frequency. A BNG regime is built around timing and restraint. They pull in opposite directions.
| Task | Standard amenity approach | BNG-compliant approach |
|---|---|---|
| Grassland | Cut every 10 to 14 days, all season | Cut and collect once or twice a year, timed after seed set |
| Arisings | Mulch and leave, or blow off | Remove arisings to reduce soil fertility |
| Hedgerows | Trim annually for tidiness | Cut on rotation, outside nesting season, allow growth |
| Wildflower areas | Overseed to fill gaps, water and feed | No fertiliser, manage for low fertility and species diversity |
| Scrub and margins | Strim back to the fence line | Retain buffer strips and structural variety |
| Deadwood | Remove and chip | Retain habitat piles where safe |
| Record keeping | Job sheet marked complete | Dated evidence, species notes, photographic record |
The most common failure we see is enthusiasm. A new site manager arrives, decides the meadow looks scruffy in July, and instructs the grounds team to cut it. One well-intentioned cut at the wrong moment can remove a season of seed set and knock the habitat back below its target condition. The units are lost, the monitoring report says so, and the LPA has a question.
The second most common failure is documentation. The work gets done properly, but nobody records it in a form that survives a change of contractor or a change of facilities manager. When the year-five condition assessment happens, there is no evidence trail.
Not meeting your BNG requirements can put you in breach of planning conditions, planning obligations or your legal agreement, and the local planning authority can take enforcement action.
The LPA is expected to monitor gains secured by planning obligations and to consider enforcement where obligations are not being met. Enforcement practice across authorities is still maturing, and there is honest debate in the planning profession about how proactively councils will police 30-year commitments. But “the council probably will not check” is a poor foundation for a liability that outlives most commercial leases.
There is also a commercial dimension that has nothing to do with enforcement. BNG performance increasingly shows up in ESG reporting, in tender scoring for public sector work, and in due diligence when a site is sold or refinanced. A site with a clean, evidenced BNG record is easier to transact than one with a gap in the paperwork.
Kent County Council officially launched and published the Kent and Medway Local Nature Recovery Strategy on 5 December 2025, becoming the 18th of 48 strategies produced across England under the Environment Act 2021. Defra appointed KCC to lead it in 2023.
Why this matters commercially: strategic significance is one of the components used to calculate biodiversity units. The LNRS local habitat map now informs how strategic significance is assigned across Kent and Medway, superseding the earlier interim guidance. In plain terms, habitat created in a location the strategy has identified as a priority can be worth more units than the same habitat created somewhere the strategy has not prioritised.
The strategy is voluntary in itself, but it guides local planning decisions and steers BNG funding from new development toward the actions that benefit nature most. It will be reviewed and republished on a cycle of every three to ten years.
For Kent commercial property, that gives you two practical opportunities:
If you are procuring or renewing grounds maintenance on a site with a BNG obligation, build these into the specification.
Ask for the HMMP up front. Any contractor pricing a BNG site without reading the HMMP is guessing. If nobody can find it, that is your first job, not theirs.
Specify outcomes, not just visits. “Twelve cuts per season” is the wrong unit of measurement for a meadow. “Achieve and maintain the target condition set out in the HMMP” is right, with the schedule that supports it.
Budget for the awkward years. Years one to three are the expensive ones. Establishment, failure replacement, weed pressure and irrigation in dry summers all land early. Costs then settle. Pricing a flat annual figure across 30 years tends to underfund the establishment phase and then overfund the plateau.
Make record keeping contractual. Dated task records, photographs from fixed points, species observations, and a note of anything that failed. This is what turns into your monitoring report.
Agree who talks to the ecologist. Condition assessment is an ecologist’s job, not a grounds team’s. But the ecologist needs the grounds team’s records to assess anything meaningfully. Someone has to own that handoff.
Plan for contractor changeover. In 30 years you will change contractor several times. Insist that the record set belongs to you, not to the incumbent.
You can read more about how we structure long-term contracts in our commercial grounds maintenance guide, and our guide to commercial grass cutting costs and frequency sets out how mowing regimes are priced across a season. [PUBLISHING NOTE: once Blog 8 is live, add a link here to the commercial grounds maintenance cost guide with the anchor “what grounds maintenance actually costs”.]
Who is legally responsible for maintaining Biodiversity Net Gain habitat?
The landowner. Government guidance states the land owner is legally responsible for creating or enhancing habitat and managing it for at least 30 years to achieve the target condition. That responsibility is secured through a planning condition, Section 106 agreement or conservation covenant and runs with the land, so it passes to a new owner on sale.
How long does BNG habitat have to be maintained?
A minimum of 30 years for off-site gains and significant on-site gains, starting from completion of the development. Where habitat creation itself takes time, such as a year of tree planting, pond digging or seeding, the clock starts on completion of that work.
Does a grounds maintenance contractor need special qualifications for BNG work?
There is no single mandatory BNG certificate for contractors. What matters is demonstrable capability: understanding of habitat condition criteria, correct timing around nesting and seed set, appropriate machinery for cut-and-collect regimes, competent record keeping, and recognised quality and environmental management systems such as ISO 9001 and ISO 14001.
Is my site exempt from BNG after the August 2026 changes?
Developments of 0.2 hectares or below are exempt from mandatory BNG for planning applications made from 6 August 2026, unless the development negatively affects on-site priority habitat. The exemption applies to new applications only. If your site already has a BNG obligation secured through an existing permission or legal agreement, that obligation stands.
What is the difference between a Biodiversity Gain Plan and an HMMP?
The Biodiversity Gain Plan is submitted to the local planning authority and shows how the development will achieve its BNG requirement. The LPA must approve or refuse it within 8 weeks, and approval is required before development can start. The Habitat Management and Monitoring Plan is the longer-term document that sets out how the habitat will be managed and monitored across the 30-year period.
Can normal grass cutting damage BNG compliance?
Yes. Cutting created grassland on a standard amenity frequency, or at the wrong point in the season, can prevent seed set and push habitat below its target condition. This is the single most common way sites lose biodiversity units after handover.
Does the Kent and Medway LNRS change what I have to do?
The strategy itself is voluntary, but it informs local planning decisions and the strategic significance component of the biodiversity metric across Kent and Medway. Habitat created in areas the strategy identifies as priorities can carry greater weight.
Blue Harbour Estates delivers long-term grounds maintenance and arboriculture across Kent, London and the South East, including Canterbury, Maidstone, Tunbridge Wells and the Medway towns. We work to ISO 9001:2015 and ISO 14001:2015, and hold Constructionline Gold, SSIP, Achilles Silver+ and Avetta accreditation, which means the record keeping and environmental management systems your BNG obligation depends on are already in place.
If you have a site carrying a 30-year habitat commitment and you are not confident it is being managed to the plan, we will review the HMMP with you and tell you plainly what needs to change. Read more about our approach on our sustainability page, or get in touch for a site review.
Author byline suggestion: reviewed by the Blue Harbour Estates operations team, Gillingham, Kent. Blue Harbour Estates Services Ltd is ISO 9001:2015 and ISO 14001:2015 certified.
