Nutrient neutrality means you have to prove your scheme adds no extra nitrogen or phosphorus to a protected site that is already failing because of nutrient pollution. If it applies to your site, the council cannot grant permission until you have shown it — and that is true of a single barn conversion as much as a 200-home scheme.
Defra’s guidance puts the footprint at 31 habitats sites, spanning 27 catchments and 74 local planning authorities. This guide covers what triggers it, what changed when the Planning and Infrastructure Act 2025 became law, and the routes to clearing a site while that new system is still being built.
What triggers nutrient neutrality
The obligation comes from regulation 63 of the Conservation of Habitats and Species Regulations 2017. Where a protected site is in unfavourable condition because of nutrients, the council has to carry out an appropriate assessment before it can authorise anything that would add to the load. It can only grant permission if it is satisfied there is no adverse effect on the site’s integrity.
The reason a small scheme gets caught is that the assessment is about what leaves your site through the sewer. Anything that creates overnight accommodation — a new dwelling, a self-build, a barn conversion, a holiday let, student rooms, a care home — increases the population served by a treatment works discharging into the catchment. Commercial floorspace with no residential element usually does not.
Catchments follow water, not administrative boundaries. A site can be several miles from the protected river and still drain into it, and a site the other side of a watershed from a river it overlooks may be outside. This is why the check has to be a map check rather than a guess.
What the Planning and Infrastructure Act 2025 changed
The Planning and Infrastructure Act 2025 received Royal Assent on 18 December 2025. Part 3 creates a new route out: Natural England prepares an Environmental Delivery Plan for an area, the Secretary of State makes it, and a developer inside it discharges the obligation by paying a nature restoration levy instead of sourcing mitigation itself.
The August 2026 NPPF recognises this. Policy N6(1)(a) says a proposal affecting a habitats site should be refused unless an appropriate assessment concludes there is no adverse effect on integrity, the derogation tests are satisfied, or the impact “is being addressed through an Environmental Delivery Plan which has been made and the developer has committed to paying the nature restoration levy”.
None of that helps you yet. Natural England notified the Secretary of State in December 2025 of its intention to prepare 23 EDPs, 16 of them for nutrient pollution. The operating regulations — the Nature Restoration Levy Regulations 2026 and the Environmental Delivery Plans (Appropriate Prioritisation) Regulations 2026 — were laid before Parliament on 18 June 2026. As at September 2026 no nutrient EDP has been made. Until one covering your catchment is made, the obligation is unchanged and you mitigate the old way.
The 2030 upgrade date, and what you can already assume
Section 168 of the Levelling-up and Regeneration Act 2023 inserted sections 96A to 96G into the Water Industry Act 1991. In a designated sensitive catchment area, a sewerage undertaker must bring every treatment works with a capacity above a population equivalent of 2,000 up to the nutrient pollution standard — total nitrogen no more than 10 mg/l, total phosphorus no more than 0.25 mg/l — by the upgrade date.
Defra designated the catchments in the Notice of Designation of Sensitive Catchment Areas 2024, effective 25 January 2024, with the Somerset Levels and Moors added on 16 May 2024. The upgrade date is 1 April 2030. The designated catchments include Poole Harbour, the Solent, the River Avon, the Axe, the Camel, the Derwent and Bassenthwaite Lake, the Eden, the Itchen, the Kent, the Lambourn, the Mease, the Wensum, the Somerset Levels and Moors, Stodmarsh, Teesmouth and Cleveland Coast, and parts of the Broads.
Section 169 and Schedule 15 of the same Act require the competent authority to assume, when it carries out the habitats assessment, that the upgrade will be delivered by that date. In practice that shrinks the nutrient budget you have to mitigate, because the headroom created by the upgrade is treated as real. It does not remove the obligation, and it does nothing for a catchment that was never designated.
Outline permission is not a shield
In C.G. Fry & Son Ltd v Secretary of State for Levelling Up, Housing and Communities [2025] UKSC 35, handed down on 22 October 2025, the Supreme Court held that regulation 63 does not stop at the grant of outline permission. It applies at reserved matters and at discharge of conditions, wherever that decision is what actually authorises the project to proceed — even where the outline permission predates the advice that created the problem.
If you are buying a site with an outline consent granted before its catchment was flagged, that consent is not the clean asset it looks like. Price the mitigation, or price the risk that the council cannot lawfully discharge the conditions without it.
Fry did win a narrower point: Ramsar sites were protected by policy rather than statute, so they could not be reopened at discharge stage. That gap has since closed. Part 1 of Schedule 5 to the Planning and Infrastructure Act 2025 came into force on 21 May 2026 under SI 2026/549, putting Ramsar sites in England on the same statutory footing as European sites. The amendments do not apply to a project authorised by a planning permission granted before 17 August 2020.
How to clear a site inside a nutrient neutrality catchment
You need a nutrient budget, calculated on the council’s catchment calculator, and then enough mitigation to bring it to zero or below. There are three routes, and most schemes use more than one.
- On-site. A package treatment plant rather than a connection, a wetland or reed-bed, sustainable drainage, or taking land out of agricultural production within your own holding. Realistic on a site with spare land, rarely enough on its own for a dense scheme.
- Credits from a private scheme. A landowner or broker converts land within the same catchment — typically arable to woodland, wetland or extensive grassland — and sells the nutrient load avoided as credits. Availability and price vary sharply by catchment and there is no national price list, so get a written quote before you commit to a purchase price for the land.
- A council or Natural England scheme. Several authorities in affected catchments run their own mitigation schemes. Natural England’s Nutrient Mitigation Scheme still operates alongside them, on a cost-recovery basis, and Natural England has said it intervenes where the private market has not delivered.
Whichever route, the mitigation has to be legally secured for the lifetime of the development, normally through a section 106 agreement or a conservation covenant, and it has to be additional — something that would not have happened anyway. A verbal arrangement with a neighbouring farmer is not mitigation.
Nutrient neutrality is not biodiversity net gain
These get confused, and the confusion is expensive. They are separate obligations with separate accounting, and satisfying one does nothing for the other. Biodiversity units do not offset a nutrient load; nutrient credits do not generate biodiversity units. The same field can be used to produce both only where the scheme has been designed and secured to deliver both, and it is usually priced accordingly.
Note also that the new BNG exemption for sites of 0.2 hectares or below, which came into force on 6 August 2026, is an exemption from BNG only. It has no effect on nutrient neutrality. A 0.15-hectare plot in the Solent catchment still needs a nutrient budget.
Check the catchment before you offer
The one mistake that reliably costs money is finding out after exchange. Natural England’s Nutrient Neutrality Catchments (England) dataset is published openly and was last updated in May 2026. Catchment boundaries do move — Natural England notified Cumberland Council of a substantially reduced sensitive area for the River Eden SAC in February 2026 — so check the current boundary rather than a copy in an old report.
In BOOM!, nutrient neutrality catchments are a Data Studio layer and a SiteSeeker constraint, so you can see the boundary on the map or exclude affected land from a search before you look at a single title.
The same discipline applies to the designations that sit underneath these catchments. If your site drains into one, it is worth understanding the Special Area of Conservation or SSSI that the catchment exists to protect, because the same appropriate assessment will deal with recreational pressure and air quality alongside nutrients.
