Identifying the planning unit in a change of use case

Before you can say whether a material change of use has occurred, you have to say what land you are looking at. Section 55(1) of the Town and Country Planning Act 1990 makes the making of any material change in the use of buildings or other land development, and materiality is judged by comparing the use of the planning unit before and after. Draw the unit wrongly and the answer comes out wrongly, however careful the use class analysis that follows.

This is the step most often skipped in a planning statement, and it is the step an officer or an inspector will test first when the answer is contentious.

Why the unit decides the question before the use class does

Take a builder's yard of 0.6 hectares with an office at the front. If the whole site is one planning unit with a single main purpose, adding a small trade counter changes the character of that unit hardly at all. If the office is a separate unit, converting it to a retail shop is a change of use of the whole of that unit, and it is plainly material.

Same physical change. Different answer. The reason is that materiality is assessed against the character of the unit as a whole, so the size of the unit sets the denominator.

That is also why intensification arguments so often fail. An increase in the scale of an existing use within a properly identified unit rarely amounts to a change in the character of that use, unless the increase brings a different use into being altogether.

Unit of occupation as the starting point

The working framework comes from Burdle, decided in 1972, where Bridge J set out three situations. It remains the standard reference in decisions and appeals.

Where a single main purpose of the occupier's use can be recognised, with secondary activities incidental or ancillary to it, the whole unit of occupation is the planning unit. Where the occupier carries on a variety of activities and none can be described as ancillary to another, the whole unit of occupation is still usually the right unit, and the use is a composite one. And where, within a single unit of occupation, two or more physically separate and distinct areas are occupied for substantially different and unrelated purposes, each of those areas is a separate planning unit.

So the enquiry runs in this order:

1. Identify the unit of occupation, which is normally the extent of the land in one person's or one entity's occupation.
2. Ask whether there is a single main purpose with ancillary activities.
3. If there is not, ask whether the activities are functionally linked, making a composite use.
4. If they are unrelated and occupy physically separate and distinct areas, split the unit.

Occupation, not ownership. A landlord's freehold across a parade of six shops is one ownership and six planning units.

Physically separate areas within one occupation

The third Burdle situation is the one that generates argument, because "physically separate and distinct" and "substantially different and unrelated" both take work.

Evidence that supports a split: separate access from the highway, no internal connection, a physical boundary such as a wall or fence, separate services and metering, separate rating assessments, distinct operational management, and a use that would function unchanged if the other stopped.

Evidence against a split: shared parking, shared welfare facilities, staff moving between the areas during a working day, one set of accounts, and a functional dependence in either direction. A farm shop selling produce grown on the holding is functionally linked to the farm. A farm shop selling bought in goods to passing traffic, fenced off with its own car park, is heading towards a separate unit.

Keep the two limbs apart in the analysis. Areas can be physically separate and still functionally linked, in which case they remain one unit.

Composite and mixed uses

A composite use is a single unit with two or more primary activities, neither ancillary to the other. The consequence is significant: within a composite use, the relative intensity of the component activities can fluctuate without a material change of use occurring, provided the overall character of the composite use is unchanged.

That gives a landowner real flexibility, and it also means the baseline has to be described carefully. A unit described in a certificate as "mixed use for vehicle repair and vehicle sales" is a much more useful asset than two certificates for two separate units.

The limit is character. If one component grows until it dominates and the other becomes vestigial, the character of the composite use has changed, and that can be a material change even though both activities were always present.

Subdivision and the creation of new units

Subdivision cuts both ways in the legislation. Section 55(3)(a) puts the matter beyond argument for dwellings: the use as two or more separate dwellinghouses of a building previously used as a single dwellinghouse involves a material change of use. So splitting a house into flats is always development, whatever the physical works.

For commercial premises there is no equivalent provision. Subdividing a large retail unit into three smaller ones may involve no material change of use at all if each remains within the same use class and the character of the area is unaffected, though it can still require permission for the physical works and it often raises servicing and access issues that a Transport Statement will need to address.

Watch the opposite direction too. Amalgamating two units into one creates a single larger planning unit, which resets the baseline for any future intensification analysis.

Applying the test to a shop with a flat above

The classic worked example, and worth setting out properly.

If a shopkeeper occupies both the ground floor shop and the flat above, with internal access and no separate letting, the planning unit is the whole building and the use is a mixed or composite retail and residential use. There is no separate Class C3 dwelling to lose.

If the flat is let separately, with its own front door, its own council tax band and its own services, there are two planning units: a Class E or sui generis unit below and a Class C3 dwelling above. That matters for at least three things. Permitted development rights attaching to a dwellinghouse are not available to a flat. A prior approval route for commercial to residential conversion applies to the commercial unit only. And the loss of the flat becomes a loss of housing, engaging development plan policy.

The evidential work is unglamorous: leases, council tax records, rating list entries, utility accounts, electoral roll entries, and photographs of the access arrangement. Where the history is unclear, the answer is often a certificate application rather than a full application, and the guide to evidencing a lawful use where the history is silent sets out what a council will accept.

Setting out the unit in a submission

Do it explicitly, near the front of the Planning Statement, under its own heading. Include a plan with the unit outlined and the occupation stated, then the evidence, then the conclusion on whether the unit is single purpose, composite or split.

Two cautions. The red line on your application form is not the planning unit. It is the land you are asking about, and an officer is entitled to conclude that the relevant unit is larger or smaller. And a conclusion on the planning unit reached for one purpose binds nobody later, so a helpful answer on this application can become an unhelpful precedent on the next one. Where certainty matters, apply for a certificate of lawful existing use under section 191, which produces a determination on the facts.

Conditions can also cut across all of this, because a condition restricting the use of part of a site can prevent a change that the use classes would otherwise permit, as the note on conditions that remove Class E flexibility explains. Read the whole planning history before you draw the line.

Draft the planning unit analysis and the rest of your statement on PlanScope, then have it reviewed before submission.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.