Net gain on outline permissions and phased schemes

On an outline permission or a phased scheme, the biodiversity gain condition works differently. Instead of one plan approved before work starts, the regime is modified so that an overall plan covers the whole development and a separate plan covers each phase, approved before that phase begins.

That structure suits a build-out over ten years, and it also creates a set of traps around baselines, unit allocation and what happens when a later parcel is sold to somebody else.

How the regime treats an outline consent

An outline permission is still a planning permission, so the deemed biodiversity gain condition attaches to it in the ordinary way where the regime applies. What changes is the mechanics.

The modifications for phased development require an overall biodiversity gain plan setting out how the gain objective will be met across the whole development, and then a plan for each phase before that phase starts. The local planning authority approves each in turn.

For a scheme consented in outline with all matters reserved, the overall plan has to work from parameter plans rather than from a detailed layout. That is possible, and it means the parameter plans have to carry more information than developers are used to putting in them: the extent of retained habitat, the green infrastructure corridors, the areas set aside for creation, and the land that will be developed.

Where those parameters are drawn loosely, the reserved matters submissions will not match the overall plan, and the phase plan is where that shows up.

The overall plan and the phase plans

Think of the overall plan as the strategy and the phase plans as the delivery.

The overall plan needs the baseline for the whole site, the proposed post-development position, the split between on-site creation, off-site units and any credits, and the way the habitat is distributed across the site. It also needs a management approach for on-site habitat over 30 years.

A phase plan then shows what that phase does: the habitat it removes, the habitat it creates, the units it contributes or consumes, and how the phase sits within the overall position. It has to be approved before that phase begins, so the programme has to allow for determination each time.

Keep one metric file as the master and version it per phase. Separate files maintained by different consultants over eight years diverge, and the authority will notice when the phase 4 baseline does not match the phase 1 output.

Fixing the baseline across a long build out

The pre-development biodiversity value is assessed as at the relevant date for the permission, not as at the start of each phase. A site that was arable in 2026 is still assessed as arable when phase 5 starts in 2034, even if that parcel has been a haul road for five years.

This is the provision that makes phased development workable, and it needs the evidence to survive. Keep the original survey report, the parcel mapping, the photographs and the metric file in a form that somebody can open in a decade. The ecologist who did the baseline will have moved firms.

Habitat cleared or degraded after 30 January 2020 is valued as it was immediately before the clearance, so early enabling works do not reduce the baseline in your favour.

One practical consequence is worth planning for. Where a later phase will be built on land used as a compound, the restoration of that land to the habitat assumed in the overall plan is part of the delivery, and it needs to appear in the phase plan and the construction management arrangements.

Allocating units between phases

The arithmetic across phases is where schemes come unstuck. Habitat created in phase 1, on land inside phase 1, may be the thing that allows phase 4 to work. If phase 1 is built and the habitat is not delivered, the later phases have no route to approval.

Three rules that keep it honest. Deliver habitat in the phase where it is created rather than deferring it. Record in the overall plan which phase each parcel of created habitat is attributed to. And where units are borrowed from a later phase, say so explicitly rather than leaving the reader to reconcile two spreadsheets.

Off-site units add another layer. They are allocated to a permission on the biodiversity gain sites register, and where a scheme is phased the allocation has to reflect the phasing. Buying the whole allocation up front is simpler administratively and ties up capital, and buying phase by phase risks the units being unavailable at the price assumed. That is a commercial judgement rather than a planning one, and it should be made deliberately.

A Biodiversity Net Gain Assessment must be prepared by a competent person under the Environment Act 2021 regime. An AI-drafted document can structure the work and flag the facts it does not hold, and the metric and the judgement remain with that person.

Delivering habitat early and the time penalty

The metric penalises delay. Habitat that takes years to reach its target condition scores fewer units than habitat that gets there quickly, and creation that starts late in the programme carries a further reduction for the time between the baseline and the delivery.

So early delivery is worth real units. Planting the structural landscape in the first phase, ahead of the homes it serves, improves the metric position and gives the scheme something to show at the sales suite.

It also reduces risk. Habitat delivered in year one has 30 years of management starting from year one, and the monitoring record builds from a known starting point rather than from a deferred promise.

The Landscape Strategy should therefore be programmed alongside the infrastructure, not treated as the last item before handover. Where the two documents disagree about what is planted where, the authority follows the approved gain plan.

Reserved matters and keeping the parameter plans honest

Every reserved matters submission is a chance for the layout to drift away from the overall plan. A road realigned by 15 metres, a plot boundary pushed into a margin, an attenuation basin moved: each changes a habitat parcel.

Build the check into the reserved matters process. Before each submission, run the layout against the metric parcels and confirm that the areas still hold. Where they do not, revise the overall plan at the same time rather than waiting for the phase plan to fail.

Set out the position in the Planning Statement accompanying the reserved matters, with a short section confirming consistency with the approved gain plan. Officers value that, and it takes a paragraph.

Selling phases and who carries the obligation

The condition attaches to the permission and binds the land, so a purchaser of a later parcel takes it on. What the purchaser needs, and frequently does not get, is the evidence: the approved overall plan, the metric file, the phase attributions, the off-site allocation and the management obligations already running on the retained land.

Where the retained habitat sits on land the seller keeps, the buyer's phase depends on somebody else's performance. That needs an agreement between the parties, and it should be drafted at the point of sale rather than discovered during the phase plan application.

Sale of part also raises the question of who holds the 30-year management obligation, whether it sits with a management company, and how the monitoring reports reach the authority. Settle it in the section 106 or the covenant rather than leaving it to goodwill.

One honest uncertainty: practice on how much detail an overall plan needs at outline stage still varies between authorities, and there is limited published guidance. Ask the authority's ecologist what they expect, and get the answer in writing before the outline application is submitted.

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