Severance: when one permission cannot be built in parts
A planning permission is normally a permission for the whole development, not a set of independent parts. Here is what severance means, where the rule comes from, and how to check the position for a part-built site.
Severance, in planning, is the question of whether one planning permission can lawfully be built in separate parts, with some parts delivered under that permission and the rest under a later one. For most multi-unit schemes the answer is no. A permission authorises the whole development set out in the description of development and shown on the approved plans, and the Supreme Court has confirmed that such a permission is not severable unless its own wording makes it so. That becomes a live problem the moment you want to change one phase of a consented site.
The consequence is blunt. If what has already been built, together with what is now proposed, means the approved scheme can no longer be completed as approved, further works under the original permission are unlawful.
What severance means for a planning permission
A severable permission is one drafted so that each identified part of the development stands on its own and can be begun, built and finished independently of the others. Read the description of development first, then the conditions, then the approved drawings. If those documents describe a single integrated scheme, with a site-wide access, a site-wide drainage layout and a landscape plan that only works as a whole, the permission is very unlikely to be severable.
Severability is not a matter of intention. It is a matter of construction of the permission as a public document, judged by what a reasonable reader with the approved plans in front of them would understand.
Very few permissions are drafted as severable. A small number are, usually where an authority has deliberately described two or more self-contained parcels and conditioned them separately. If yours does not say so, assume it does not.
Where the rule comes from
Two decisions carry the weight. In Pilkington v Secretary of State for the Environment (1973) the court dealt with two permissions on one plot, each for a bungalow in a different position. Once the first was built, the second could no longer be carried out as approved, because the land needed for it had gone. The principle that emerged is physical impossibility: a permission cannot be implemented if the development it describes can no longer physically be completed.
Hillside Parks Ltd v Snowdonia National Park Authority [2022] UKSC 30 applied that to the modern multi-phase estate. The court held that a permission for a development of several buildings is not normally severable, that later permissions for parts of the same land do not amend or replace the earlier one, and that development carried out under the original permission becomes unlawful once the approved scheme has been rendered physically impossible.
So the statutory routes matter more than the drop-in habit that grew up before 2022.
| Route | What it does | Typical use |
|---|---|---|
| Section 96A, Town and Country Planning Act 1990 | Non-material amendment to an existing permission | Minor plan corrections, small dimensional changes |
| Section 73 | New permission varying or removing conditions, including an approved-plans condition | Changes that are not a fundamental departure from the description of development |
| Section 73B (inserted by the Levelling-up and Regeneration Act 2023) | New permission varying an earlier one where the effect is not substantially different | Check whether it is in force, and the accompanying guidance on gov.uk, before relying on it |
| Fresh full application for the whole site | A new permission covering the amended scheme in its entirety | Where phases have diverged materially from the approved layout |
The fourth row is the one most people resist and most often need. A fresh application for the whole site, with an amended masterplan, puts the development back on a single lawful footing and removes the argument entirely.
How an authority or inspector applies it
The test is applied to the approved drawings, not to the marketing brochure. An officer asked to confirm that works may continue will compare the as-built position against the approved layout and ask whether the remainder of the approved development can still be delivered.
Minor departures do not bite. The Supreme Court accepted that a permission can still be implemented where what has been done departs from the approved plans in a way that does not amount to a material difference from the development as a whole. The difficulty is that nobody wants to find out where that line sits through enforcement proceedings or a refused building control completion.
Two practical signals that you are in trouble. First, a later permission has been granted for a parcel inside the red line of an earlier unimplemented or part-implemented permission, with a different access, plot layout or drainage route. Second, the approved site-wide landscaping, open space or affordable housing plots have been built over.
An illustrative example
The following is illustrative only and not a real case.
A 60 unit scheme is permitted in 2019 with a single approved layout, a condition tying development to the approved drawings, and a section 106 obligation delivering 18 affordable units in plots 31 to 48. Phases one and two, plots 1 to 30, are built out as approved. The market then moves and the developer secures a separate permission in 2024 for 22 apartments on the land occupied by plots 31 to 48.
Building those apartments makes the 2019 layout impossible. Plots 49 to 60, still unbuilt, now have no lawful permission to rely on, because the 2019 permission can no longer be completed as approved. The affordable housing obligation remains binding on the land and still refers to plots that will never exist.
The fix is not elegant. A fresh application covering the whole site, an amended masterplan, a deed of variation to the obligation, and a recalculation of the levy liability on the revised floorspace. The cost of doing that at the outset would have been a fraction of the cost of doing it after the apartments were under way. A clear Planning Statement explaining the relationship between the old and new permissions is the document that carries the argument.
What severance is confused with
Phasing conditions. A phasing condition divides the delivery of one permission into stages. It does not make the permission severable. The development remains a single whole that must eventually be completed as approved.
Outline permission and reserved matters. An outline permission with phased reserved matters is still one permission. Each reserved matters approval must sit within the parameters already fixed, and a technical details consent under the permission in principle route works on the same logic.
Multiple permissions on one site. You may hold several permissions over the same land. All of them stay extant until one is implemented in a way that makes the others physically impossible. That is the Pilkington point rather than the severance point, though the two travel together.
Operational development and the material start. Whether works amount to a lawful start is a separate question under section 55, covered in more detail in this explainer on operational development. A lawful start does not cure a later impossibility.
Severance of an enforcement notice. Inspectors can vary or correct part of a notice. Same word, different doctrine.
Checking the position before you build
Work through this in order, and do it before the next phase goes on site rather than after.
- Pull the full decision notice, every condition, the approved drawings list and any subsequent section 73 or section 96A approvals, and build one chronological bundle.
- Read the description of development. Decide whether it describes one development or separately identified parts.
- Overlay the as-built survey on the approved layout and mark every divergence, including levels, access geometry, plot positions and drainage runs.
- Ask the direct question for each unbuilt parcel: can the approved development still be completed as approved?
- If the answer is no, choose a route from the table above and take advice on the obligation and levy consequences before submitting.
- Record the conclusion in writing. If a future purchaser or funder asks, the file needs to show the analysis, not a view.
Most of this is a desktop exercise that a planning consultant can do in a day or two on a well documented site. On an estate consented in stages since the 1990s it takes longer, and the drawings register is usually the hardest part to reconstruct. That is the honest uncertainty here: on older sites the approved plans are sometimes ambiguous on their face, and the only safe answer is a fresh permission for the whole.
If you are assembling the evidence base for that fresh application, browse the 66 report types by category to work out what the authority will expect alongside the amended masterplan, or enter your postcode on PlanScope to see which reports the site is likely to need.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Is a planning permission severable by default?
No. A permission for a multi-unit development is normally treated as authorising the whole scheme described in the description of development and shown on the approved plans. It is severable only where the permission itself, read with its conditions and drawings, identifies parts that can each be built independently. That drafting is rare, so the working assumption should be that your permission is not severable.
What did Hillside Parks decide about drop-in permissions?
The Supreme Court held in 2022 that a later permission for part of a site does not amend or replace an earlier permission over the same land. If building the later scheme makes the earlier approved development physically impossible to complete, further works under that earlier permission are unlawful. The practice of granting standalone drop-in permissions inside a consented masterplan is therefore unsafe.
Does a phasing condition make a permission severable?
It does not. A phasing condition controls the order and timing of delivery within one permission. The development still has to be completed as approved, and a phase that departs materially from the approved layout can put the remaining phases at risk. Severability depends on how the description of development and the plans define the scheme, not on phasing.
How do I lawfully change one phase of a consented site?
Options run from a section 96A non-material amendment, through a section 73 application varying the approved-plans condition, to a fresh full application covering the whole site with an amended masterplan. Section 73B was inserted by the Levelling-up and Regeneration Act 2023 and whether that section is in force should be checked on gov.uk. On a materially changed layout, the whole-site application is usually the only clean answer.
What happens to a section 106 obligation if the layout changes?
The obligation runs with the land and keeps referring to the plots and triggers written into it. If those plots no longer exist under the revised layout, the obligation does not fall away. A deed of variation is needed, and the levy liability should be recalculated against the revised floorspace before the new permission is implemented.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.