Where your units come from changes how many you need
The metric applies a spatial multiplier to off-site gain. Units further from your development are worth less, so the cheapest unit is not always the cheapest answer.
Two habitat banks can offer units of the same habitat, in the same condition, at the same price per unit, and still land you with two different bills. The difference is geography, and the metric builds it in deliberately.
The spatial risk multiplier
Off-site gain is discounted according to how far it sits from the development it is compensating for. Broadly:
- inside the same local planning authority area, or the same National Character Area, as your development: no reduction
- in a neighbouring local planning authority or National Character Area: a reduction of a quarter
- anywhere else in England: a reduction of a half
That last line is the one worth staring at. Units bought a long way from your site deliver half the value they would deliver locally, so you need roughly twice as many of them. A unit priced 30% below the local market is not a saving if it is being halved on arrival.
The reasoning is sound: biodiversity net gain is meant to compensate for harm where the harm happens. A nightingale displaced in Sussex is not compensated by scrub in Northumberland.
Strategic significance
The metric also rewards habitat that is doing what the local strategy asked for. Where a site is identified in a Local Nature Recovery Strategy or another relevant plan, its units carry an uplift; where it is not, they do not. It is a smaller effect than the spatial multiplier, but it runs the same direction. Habitat in the right place is worth more than habitat merely somewhere.
Distinctiveness, and what you are allowed to trade
You cannot compensate for anything you like with anything you like. The trading rules work down from the habitat lost:
- Very high distinctiveness habitat cannot be traded away at all. It needs bespoke compensation, agreed case by case.
- High distinctiveness habitat has to be replaced with the same habitat type.
- Medium distinctiveness habitat has to be replaced with the same broad habitat group, or something better.
- Low and very low habitat can be replaced with anything of the same or higher distinctiveness, which, since almost everything is higher, is the flexible end.
Irreplaceable habitats, meaning ancient woodland, ancient and veteran trees and the rest of the list, sit outside this entirely. They are not tradeable, and any scheme affecting them is in a bespoke conversation with the authority, not a units conversation.
Trading up is always permitted. Compensating a low-distinctiveness loss with higher-distinctiveness gain is allowed, and where the numbers work it is often how a difficult metric gets resolved.
What this means when you are buying
Ask three questions about any off-site units offered to you:
- Which local planning authority and National Character Area is the site in, and how does that sit relative to my development?
- Is the habitat type right for what I am losing under the trading rules?
- Is the site registered, and can the units be allocated to my development?
A cheap unit that fails any of those is not cheap.
The honest version
Proximity is not something a seller can conjure. What a seller can do is be straight with you about where its sites are, what they generate, and how that interacts with your particular development — before you have spent time on a route that does not work.
Tell us where your site is and we will tell you what multiplier would apply and what that means for the number of units you actually need to buy.