Severability of a planning permission

A severable planning permission is one that can lawfully be implemented in part, with some elements built and others abandoned, and the starting position in English law is that a permission is not severable. A permission authorises a development, singular. You build what was approved, or you have built something that the permission does not authorise.

The Supreme Court settled the modern position in Hillside Parks Ltd v Snowdonia National Park Authority in 2022, and the practical consequences for phased sites, drop-in permissions and section 73 applications are substantial.

What severability means in practice

The question arises whenever a developer wants part of a permitted scheme rather than all of it, or wants to change one part while keeping the rest.

On a single building the answer is obvious. You cannot build the ground floor of an approved block and declare the permission half implemented. On a 200 home scheme across 20 hectares with phased infrastructure, the intuition runs the other way, and that intuition is where the trouble starts.

The legal test is not about size. It is about whether the permission, read as a whole with its conditions and approved plans, authorises a single integrated development or a set of separately implementable ones. Most permissions are the first.

The general rule against partial implementation

Two propositions do the work.

First, the development authorised is the development described in the permission and shown on the approved plans, read together. A departure that is material means the works are not authorised by that permission, and the test is applied to the scheme as a whole rather than plot by plot.

Second, following the long-standing line of authority, where a developer carries out works under a later permission that make it physically impossible to complete the earlier permitted scheme in accordance with its terms, the earlier permission can no longer lawfully be implemented. It is not revoked. It simply has nothing left that can be built under it.

That second point is what catches developers mid-build. The earlier permission does not die with a notice or a letter. It becomes unusable, and nobody tells you.

Permissions drafted in phases

Severability is possible where the permission provides for it, and the Supreme Court acknowledged as much. The drafting has to do the work, and a condition that merely says development may be carried out in phases is not enough on its own.

What helps:

• a defined phasing plan, approved as part of the permission, with each phase identified on a drawing
• infrastructure and access arrangements attributed to each phase, so that a phase can function independently
• conditions framed by reference to each phase rather than to the development as a whole
• express wording that each phase may be implemented independently of the others
• a scheme description that treats the phases as separate developments rather than as stages of one

What does not help is a masterplan permission with a single red line, scheme-wide conditions and a vague expectation that phases will be flexible. That is the common pattern and it is the one that produces the problem.

Drop-in permissions and the risk they carry

A drop-in permission is a fresh application for part of a larger consented site, usually to change the housing mix, substitute a building type or swap a block for a different one. It looks neat because it deals only with the part that is changing.

The risk is the one described above. Implementing the drop-in may make the original permission incapable of completion in accordance with its terms, which leaves the remainder of the site without a usable consent. On a site with 8 years of build-out remaining, that is a serious exposure, and it is not cured by the original permission still appearing on the register.

Whether the risk bites depends on how the original permission was drafted and on whether what remains can still be built as approved. The analysis is site-specific and it needs doing before the drop-in is submitted, not afterwards. Questions about what counts as a material change in the character of a development arise in other contexts too, including the issues set out in intensification and when doing more of the same becomes development.

Section 73 as the safer route

Where the aim is to change part of a consented scheme, varying the original permission is usually safer than overlaying a new one.

Section 73 of the Town and Country Planning Act 1990 allows an application to develop land without complying with a condition previously imposed, which in practice is the mechanism for varying approved plans where those plans are tied in by condition. The result is a new permission, but one that relates to the same development, which avoids the physical impossibility problem.

Section 73 has limits. It cannot be used to change the description of the development, and it cannot be used where the variation would amount to a wholly different scheme. Section 96A remains available where an amendment really is non-material. Section 73B, inserted by the Levelling-up and Regeneration Act 2023, provides a further route to vary a permission where the development would not be substantially different from the one already permitted, and its position in force should be checked before anyone relies on it.

Practical advice from anyone who has unpicked one of these: deal with the whole site in one section 73 application rather than a sequence of small ones, because a sequence recreates the same problem in instalments.

Effect on obligations and the levy

A new permission brings new financial consequences, and this is where drop-in strategies become expensive.

A section 106 agreement binds the land in relation to the permission it was entered into for. A fresh permission is not automatically caught by it, so the obligations either need a supplemental deed or a new agreement, and the authority has an opportunity to revisit the terms. On a scheme consented several years ago at a lower affordable housing requirement, that opportunity is not one a developer wants to hand over.

Community Infrastructure Levy liability is calculated for each chargeable development. A new permission creates a new chargeable development, with its own liability assessment, its own indexation and potentially a different rate if the charging schedule has changed. Existing floorspace deductions and any relief already claimed need to be re-examined rather than assumed to carry across.

Drafting to preserve flexibility

If you are promoting a large site now, build the flexibility into the original permission.

1. Define phases on a drawing and make them conditions of the permission.
2. Write every condition to attach to a phase, with triggers expressed per phase.
3. State expressly that each phase may be implemented independently.
4. Give each phase its own access and infrastructure so it can function alone.
5. Draft the section 106 with phase-based obligations and a mechanism for varying one phase without reopening the rest.
6. Keep the development description broad enough to survive detailed change, while remaining precise enough to be enforceable.

A Planning Statement for a phased scheme should set out the intended implementation structure explicitly, so that the permission and the supporting documents say the same thing about how the site will be built. PlanScope drafts one from your project answers and inserts a flag where a site fact is missing, and you can see the full set of 66 report types before you start.

Illustrative example. A consented 150 home scheme in four phases, with the developer wanting a different house type across 20 plots in phase three. A drop-in application for those plots risks the remaining phases. A section 73 application varying the approved plans condition for the whole site deals with it once, triggers a levy recalculation that can be modelled in advance, and keeps a single permission governing the land.

This is general guidance, not legal advice; severability is highly fact-sensitive and legal advice should be taken on any specific permission before relying on it. Enter your postcode on PlanScope to see which reports a site is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.