Enforcement appeals and the existence of a planning unit
Pick the wrong area and the same activity is either an ancillary use or a breach. The planning unit sits upstream of every other argument in an enforcement appeal.
The planning unit decides whether there has been a breach at all. If the correct unit is the whole property and the activity complained of remains ancillary to its main use, there is no material change of use and the enforcement notice fails on ground (c). If the correct unit is a single floor let separately for an unrelated purpose, the same activity is a change of use and the notice stands. Everything else in an enforcement appeal sits downstream of that question.
Landlords meet the point most often where part of a building has been let or used differently from the rest, and where the council has drawn its notice around the wrong piece of land.
Why the planning unit decides the breach
Section 55 of the Town and Country Planning Act 1990 defines development to include a material change in the use of any buildings or other land. Material change is a comparative exercise: use before against use after. The comparison has to be made over a defined area, and that area is the planning unit.
Choose a larger unit and an activity looks like an incidental part of an established use. Choose a smaller one and the same activity is the whole use of that unit, so any difference from what went before is a change.
An enforcement notice must state the matters that appear to constitute the breach of planning control and the land to which it relates. A notice drawn around land that is not the planning unit, or that lumps separate units together, is vulnerable, and the point goes to the substance of the alleged breach rather than to a technicality.
The test for identifying a unit
The framework comes from Burdle, a High Court decision from 1977 that remains the standard reference. It starts from the unit of occupation and sets out three situations.
Where the unit of occupation is used for a single main purpose, with other activities incidental or ancillary to it, the whole unit of occupation is the planning unit.
Where the occupier carries on a variety of activities with none dominant, and those activities are not confined to separate and physically distinct areas, the unit of occupation is again the planning unit, and the use is a composite or mixed one.
Where within a single unit of occupation there are two or more physically separate and distinct areas occupied for substantially different and unrelated purposes, each of those areas is a separate planning unit.
Three ideas do the work in practice: occupation, physical separation, and the relationship between the activities. None of them turns on title boundaries, and the registered extent of a freehold is a poor guide.
Ancillary and primary uses
An ancillary use is one that serves the main use. An office within a factory, a staff canteen, a storage area for a shop, a flat for a caretaker: each is ordinarily part of the main use and not a separate use for planning purposes.
Two things turn an ancillary use into a primary one. Scale, where the subordinate activity grows until it is no longer subordinate. And independence, where the activity starts serving people other than the main use, as when a factory canteen begins selling to the public.
Intensification can amount to a material change of use, and the argument is harder than it looks. More of the same is not automatically a change, and the authority has to show a change in the character of the use rather than simply more activity. That distinction is worth pressing where the notice alleges intensity rather than a different use.
| Scenario | Likely planning unit | Why |
|---|---|---|
| Shop with ancillary store and office above, one occupier | Whole building | Single main purpose with ancillary activities |
| Ground floor shop, upper floors let as a separate office | Two units | Physically distinct, separately occupied, unrelated purposes |
| Workshop used for repairs and for unrelated vehicle sales, mixed across the site | Whole site, composite use | Activities not confined to distinct areas |
| House with a room used as a consulting room by the resident | Whole house | Ancillary to residential use unless scale changes it |
Subdivision and the creation of new units
Subdividing a building is where the law is least intuitive.
For dwellings, section 55(3)(a) puts the matter beyond argument: the use as two or more separate dwellinghouses of a building previously used as a single dwellinghouse involves a material change of use. Splitting a house into flats always needs permission.
For other buildings and land, subdivision is not automatically a material change of use. Dividing a large warehouse into four separately let warehouse units may not change the use at all. The analysis is whether the subdivision creates units whose use differs from the use of the original unit, and that depends on what each new unit is used for.
The practical consequence for a landlord is that the leasing structure can create planning units without anyone intending it. Grant four separate leases over physically divided parts, each tenant doing something different, and you have created four planning units, each of which has to be lawful in its own right.
Evidence of occupation and control
Appeals on this point turn on documents and on what the inspector sees on site.
The evidence that carries weight:
- Leases, licences and tenancy agreements, with their plans, showing who occupies what and from when.
- Business rates records, which show how the valuation officer has treated the premises, and separate assessments are persuasive though not decisive.
- Utility accounts and meter arrangements, since separate metering supports separate occupation.
- Physical separation on site: separate entrances, locked doors between areas, fencing, separate signage and parking.
- Control of access, including who holds keys and who can enter which parts.
- Operational evidence: separate staff, separate hours, separate customers, separate deliveries.
Photographs and a measured plan matter as much as the paperwork. An inspector who walks through an unobstructed opening between two areas you say are separate units will not be persuaded by a lease plan.
Running the point on an enforcement appeal
Ground (c) of section 174(2) is the usual home for the argument: that the matters alleged, even if they occurred, do not constitute a breach of planning control. Ground (b), that the matters have not occurred, sometimes runs alongside it.
Plead it precisely. Identify the unit you say is correct, explain which limb of the Burdle analysis produces it, and set out the use of that unit before and after the matters complained of. Then explain why no material change has occurred.
Keep the grounds separate. An appellant who argues under ground (c) that there is no breach, and simultaneously under ground (d) that the breach became immune, is making two inconsistent points, and inspectors deal with that regularly without being impressed by it.
Run the fallback anyway where the facts support it. Ground (a), that permission ought to be granted, requires the fee and a planning case, and a short Planning Statement addressing the development plan gives the inspector somewhere to go if the unit argument fails. Appeal decisions on comparable facts are useful as an indication of how inspectors have approached the question rather than as precedent, which is the caution set out in using appeal decisions in a planning application.
Where a prior approval route was used over part of a building, the unit question interacts with the conditions attached to it, and appealing a prior approval refusal under Class MA covers that ground.
Where the point is unarguable
Be honest with the client about the cases where this does not work.
Where the appellant's own leases divide the building into separately occupied parts with unrelated uses, the authority will produce them, and arguing for a single unit becomes untenable.
Where physical separation is obvious on the ground, with separate street doors and no internal connection, the third Burdle situation applies and each area is its own unit.
Where a house has been split into flats, section 55(3)(a) settles it and no analysis helps.
And where the notice is drawn on the correct unit and the change of use is plain, pressing the point adds cost and risks an adverse costs award for unreasonable behaviour at an inquiry. In that position the useful work is on ground (a), on the steps required by the notice under ground (f), and on the compliance period under ground (g).
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and take legal advice on any enforcement notice before the appeal deadline passes.
Enter the property postcode on PlanScope to see which documents a retrospective application 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.
Frequently asked questions
What is the planning unit?
It is the area over which the comparison between the use before and the use after is made, so it determines whether a material change of use has occurred. The starting point is the unit of occupation, not the title boundary, and the analysis follows the three situations set out in the Burdle decision of 1977.
Does subdividing a building need planning permission?
For dwellings, yes. Section 55(3)(a) of the Town and Country Planning Act 1990 provides that using a building previously used as a single dwellinghouse as two or more separate dwellinghouses involves a material change of use. For other buildings, subdivision is not automatically a change of use and depends on what each new unit is used for.
Which appeal ground covers a planning unit argument?
Usually ground (c) of section 174(2), that the matters alleged do not constitute a breach of planning control. Ground (b), that the matters have not occurred, sometimes runs alongside it. Plead the unit you say is correct, the limb of the analysis that produces it, and the use before and after.
What evidence shows separate planning units?
Leases and licences with plans, business rates assessments, separate utility metering, physical separation such as separate entrances and locked internal doors, control of keys and access, and operational separation in staff, hours, customers and deliveries. Photographs and a measured plan matter as much as the paperwork.
Can intensification of a use be a breach?
It can, but the authority has to show a change in the character of the use rather than simply more of the same activity. That is a higher bar than councils sometimes assume, and it is worth testing where the notice alleges intensification rather than a different use.
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.