Mixed uses that become sui generis in their own right

A planning unit occupied by two uses, neither of which is ancillary to the other, has a mixed use that sits outside every class in the Use Classes Order. That is the trap. Because the unit is not within a class, the protection article 3 gives to movements inside a class does not apply, and any change in what happens there can be a material change of use requiring permission, even where both activities would individually fall within Class E.

When two uses in one unit form a mixed use

The starting point is the distinction between a primary use with something ancillary to it, and two uses running in parallel.

A shop with a stockroom, an office and a staff kitchen has one use. Those rooms exist to serve the retail operation and have no independent character. A shop with a café that draws its own customers, keeps its own hours and occupies a defined part of the floorspace is doing two things at once, and the question becomes whether the café is ancillary to the shop or a use in its own right.

The tests applied are functional and physical. Does the secondary activity exist to serve the primary one, or does it serve the public independently. What proportion of floorspace and turnover does it account for. Is it separately accessed, separately staffed, separately advertised.

Scale alone does not decide it, though scale is evidence. A café occupying 40 per cent of the floor area and generating most of the turnover is hard to describe as ancillary, whatever the signage says.

Composite uses and the planning unit

Burdle v Secretary of State for the Environment remains the framework. Where the whole of a unit is occupied for a single main purpose with activities incidental to it, there is one use. Where two or more physically separate areas are in different occupation or different use, there are separate units. And where activities occur throughout the unit without any one being incidental to another, the use of the whole is composite.

The third category is the one that produces sui generis mixed uses. Identifying it correctly is the first step in any advice on this, and the mechanics of how councils decide what they assess determine whether you are looking at one unit with a mixed use or two units with separate ones.

Getting the unit wrong at the start makes everything that follows wrong. A builder's yard with a trade counter may be one composite unit, or a storage use with a separate retail unit inside it, and the answer changes which applications are needed and which permitted development rights exist.

Describing a mixed use on the application form

Precision in the description does more work than anything else in the application.

"Mixed use" on its own is meaningless. The description should name both components and, where the balance matters, fix it: "Change of use to mixed use comprising retail (Class E(a)) and hot food takeaway (sui generis), with the takeaway limited to the rear 60 square metres as shown on drawing 104."

Three things to get right:

• name each component, with the class where one applies and "sui generis" where it does not
• tie the proportions or areas to a drawing rather than to a percentage in the text
• avoid describing the whole thing as falling within a class, because it does not

A vague description creates a vague permission, and the person who suffers is the owner trying to prove in five years what was authorised.

Why a mixed use loses class protection

Article 3 of the Use Classes Order provides that use for a purpose in a class is not to be treated as involving development if the use remains within that class. The provision operates on uses that are in a class. A composite use is not.

The consequence is that a small change in the balance between the two components can be a material change of use. Shifting from a shop with a small café to a café with a small shop is a change in the character of the use of the land, and whether it is material is a question of fact and degree rather than a question answered by the Order.

Permitted development rights fall away too. Most of the change of use classes in Part 3 of the General Permitted Development Order operate from a specified class, and a sui generis mixed use is not within one. The prior approval routes that would be available to a straightforward Class E unit simply do not apply.

Nor does the argument that both components would be permitted separately. It is the combination that is outside the Order.

The related question of whether doing more of an existing activity needs consent is a close cousin of this one, and intensification and when it needs consent covers the same fact and degree reasoning from a different direction.

Conditions fixing the proportions

Authorities granting permission for a mixed use frequently condition the split, and the drafting deserves attention because it binds the property for years.

Conditions that work are tied to a plan. "The area hatched blue on drawing 104 shall be used only for the purposes of a café and for no other purpose" is enforceable. Conditions expressed as percentages of turnover are not, because nobody will audit them.

Push back on conditions that fix the balance more tightly than the planning harm requires. Where the reason for the condition is parking generation or cooking odour, a condition on hours, covers or extraction addresses that directly, and leaves the operator room to move.

An illustrative example

A former bank in a secondary centre is granted permission for a mixed use as a bakery with a seating area and a small production kitchen supplying other outlets. The permission describes retail, café and light industrial components and fixes the production area on plan. Three years later the operator wants to double the production area and reduce the seating. Because the unit is sui generis, that shift requires a fresh application rather than falling within Class E. This example is illustrative.

Reverting to a single use later

Dropping one component does not automatically return the unit to a class.

Ceasing the café and using the whole unit as a shop is a change from a composite use to a Class E(a) use, and that is a material change of use requiring permission, unless the café element had already ceased long enough to have been abandoned or was never more than ancillary in the first place.

In practice councils often take a pragmatic view where the remaining use is obviously less intensive. But relying on that is a risk on a property being sold or refinanced, and the safe route is an application for the single use or a certificate of lawfulness confirming the position.

Where the original permission included a condition fixing the mix, that condition survives and will need varying under section 73 regardless of what the underlying use position is.

Evidence of the established mix

Proving what the lawful use is, years later, is the recurring problem, and the evidence needs assembling before anybody needs it.

1. The permission and its conditions, with the approved drawings.
2. Floor plans showing the areas in each activity at the relevant dates.
3. Trading records, staff rotas and supplier invoices distinguishing the components.
4. Photographs, menus, price lists and advertising from the period.
5. Statutory declarations from people with direct knowledge of the operation.

Where the mix has changed without permission and enough time has passed, an application for a certificate of lawfulness of existing use under section 191 of the Town and Country Planning Act 1990 is the tool. The burden sits on the applicant and the standard is the balance of probabilities, so contemporaneous documents matter more than recollection.

A planning statement that sets out the unit, the components and the evidence for each is usually the document that carries a mixed use application, and it is worth writing before the form is filled in rather than afterwards.

Browse all 66 PlanScope report types to see what a mixed use application 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.