The planning unit and why it decides the use class question
Identify the planning unit before you reach for the Use Classes Order. The occupation test, physical separation, composite uses and what the evidence has to show.
Before you can say whether a proposal involves a material change of use, you have to say what land you are looking at. The planning unit is that answer, and getting it wrong turns a straightforward use class question into a contested one. A first floor let separately is a different unit from the shop below. A workshop at the end of a garden occupied with the house is part of the same unit. The use class exercise runs on whatever the unit turns out to be, so the unit comes first.
What a planning unit is and how it is identified
The concept is judicial rather than statutory. The Town and Country Planning Act 1990 says at section 55 that development includes the making of any material change in the use of any buildings or other land, and leaves the courts to supply the framework for applying it.
The framework in daily use comes from Burdle, decided in 1972, which set out three situations:
- Where the unit of occupation is the same and the occupier's activities are directed to a single main purpose, the whole unit is the planning unit, and activities ancillary to that purpose do not count separately.
- Where the occupier carries on a variety of activities with no single main purpose and they are not confined to separate physical areas, the whole unit is still the planning unit and the use is composite.
- Where within one unit of occupation there are two or more physically separate and distinct areas occupied for substantially different and unrelated purposes, each area is a separate planning unit.
The starting point in every case is the unit of occupation. Begin there, then ask whether the third situation applies, and resist the temptation to start from the shape of the red line on a plan.
The occupation test and physical separation
Occupation does the first cut. Land held and used by one occupier is presumptively one unit, however varied the activities on it.
Physical separation does the second. To break a unit of occupation into smaller units, the areas have to be both physically distinct and used for substantially different and unrelated purposes. A yard that is fenced off and used for open storage while the building is used as offices, by the same company, is usually still one unit because the purposes are related. The same yard let to an unconnected storage business is two units.
Look for the indicators that a court or an inspector will look for: separate entrances, physical division by walls or fences, separate services and metering, separate rating assessments, separate leases, and whether one area could function without the other. None of them is decisive on its own and the rating assessment in particular is evidential rather than determinative.
The distinction between an activity that is ancillary and one that has become a use in its own right is developed in our note on ancillary use and the separate planning unit.
Why sub-division creates new units
Sub-division is the clearest way a unit changes. Split a shop into two, let them separately, and there are two planning units where there was one.
Whether that itself is a material change of use is a separate question. For dwellings, section 55(3)(a) removes any doubt by providing that the use as two or more separate dwellinghouses of a building previously used as a single dwellinghouse involves a material change in the use of the building and of each part. For commercial premises there is no equivalent provision, so sub-division is a change of use only where it produces a materially different use in planning terms, which is why sub-dividing a large retail unit into two smaller retail units is frequently not development while sub-dividing a house into flats always is.
Physical works to achieve the sub-division are a separate matter again, and may need permission as operational development even where the change of use does not.
Ancillary activities within one unit
An ancillary activity is one that is functionally subordinate to the primary use and is an ordinary incident of it. The staff canteen in a factory, the office in a builder's yard, the storeroom behind a shop. None of them is separately assessed, and none of them attracts its own use class.
Three things end that status. Growth, where the activity becomes substantial enough to be a purpose in its own right rather than an incident of the main use. Severance, where the activity is let or sold separately, because occupation is the foundation of the unit. And divergence, where the activity starts serving a different customer base, as when a factory canteen opens to the public.
Intensification is the hardest of the three to argue. A change in the degree of an existing use only becomes development where it amounts to a change in the kind of use, and inspectors are properly sceptical of intensification arguments unadorned by evidence of character change. Bring the evidence: movements, hours, staff, deliveries, noise complaints, floor areas.
Where two uses occupy the same building
The composite use is underused as a description and frequently the honest one. A building where the ground floor is a shop, the first floor is a studio and both are occupied by the same person, with internal access between them and no physical separation, is a single unit in composite use rather than two units.
The consequence matters. A composite use falls outside the Use Classes Order, so the flexibility to move between Class E uses does not apply to it. That flexibility, and its limits, are set out in our note on changes of use within Class E.
It also means the whole composite use is the baseline against which any future change is judged. An applicant who describes the building as two units to obtain a favourable comparison will find that description quoted back at them when the next application is made.
Consequences for whether a change is material
Once the unit is fixed, everything else follows from it.
| Question | How the planning unit affects it |
|---|---|
| Is there a material change of use? | Assessed across the unit as a whole, so a change affecting part of a unit may not be material at unit level |
| Does a use class apply? | Classes apply to the use of the unit; a composite use has no class |
| Are permitted development rights available? | Rights attach to the unit and its curtilage, so sub-division can remove them |
| Has the use become lawful through the passage of time? | Time runs against the use of the unit as identified |
| Is an enforcement notice valid? | The notice must correctly identify the land, and misidentifying the unit is a ground of appeal |
The enforcement point is worth dwelling on. A notice drawn around too much or too little land is vulnerable, and the planning unit analysis is often the first thing an appellant's advocate attacks.
Describing the unit on an application form
Three fields carry the analysis: the red line, the description of development, and the statement of existing use.
Draw the red line around the planning unit affected by the proposal, not around the applicant's whole landholding, and use a blue line for other land in the same ownership. Describe the development in terms that match the unit you have drawn. Where the proposal affects part of a larger unit, say so explicitly, because an officer who spots a mismatch between the red line and the description will raise it at validation.
Set out the existing lawful use in the Planning Statement rather than leaving it implied. A paragraph identifying the unit, its occupation history and its lawful use gives the officer a starting point they can adopt, and it is the paragraph an inspector will read first on any subsequent appeal.
Evidence that fixes the unit boundary
Assemble the documents before you take a view, not afterwards.
Leases and licences show the extent of occupation and the permitted use. Rating list entries show how the Valuation Office Agency has assessed the premises, which is evidential without being decisive. Utility accounts and meter positions show servicing arrangements. Historic floor plans, fire risk assessments and insurance schedules often describe internal divisions more accurately than anything drawn for a planning application. Aerial and street-level imagery over a run of years shows fences, gates and signage appearing and disappearing.
Where the lawful use of the unit is itself in doubt, resolve that first through a certificate of lawfulness under sections 191 or 192, using the approach set out in our note on proving an existing lawful use before a change of use. A change of use application built on an assumed baseline is an application built on sand.
To see which supporting documents a change of use proposal is likely to need, enter your postcode on PlanScope and run the constraint check.
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
What is the planning unit?
The area of land against which a material change of use is assessed. It is a judicial concept rather than a statutory one, derived from the Burdle decision of 1972, and it starts from the unit of occupation. Only physically separate areas used for substantially different and unrelated purposes form separate units within one occupation.
Is the rating assessment the same as the planning unit?
No, though it is useful evidence. The Valuation Office Agency assesses hereditaments for rating on its own criteria, which overlap with but do not match the planning analysis. Treat a separate rating assessment as one indicator alongside leases, entrances, services, physical division and whether each area could function alone.
Does sub-dividing a shop need planning permission?
Not automatically. Section 55(3)(a) makes sub-division of a dwellinghouse into two or more dwellings a material change of use, but there is no equivalent provision for commercial premises. Splitting a large retail unit into two retail units is often not development, though the physical works may still need permission.
What makes an activity ancillary rather than a separate use?
It must be functionally subordinate to the primary use and an ordinary incident of it, like a staff canteen in a factory. That status ends if the activity grows into a purpose in its own right, is let or sold separately, or starts serving a different customer base from the main use.
Why does a composite use matter?
A composite use falls outside the Use Classes Order, so the flexibility to move between Class E uses does not apply to it. The composite use also becomes the baseline against which any future change is measured, which is why describing a building accurately at the outset pays off later.
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.