Ancillary use and when it becomes a material change

An ancillary use needs no permission of its own because it is part of the primary use of the planning unit. The difficulty is that nothing freezes it there. An ancillary use material change happens when the subordinate activity grows, separates or intensifies to the point where it is a use in its own right, and at that moment permission is required even though nobody has done anything new on a particular day.

For a planning consultant the practical question is rarely whether something is ancillary today. It is how to evidence what it was, how to condition what it will be, and how to protect a client from an enforcement notice in three years.

What ancillary means in planning terms

A use is ancillary where it is functionally subordinate to, and serves, the primary use of the land or building. The office in a factory, the storage room behind a shop, the staff canteen in a warehouse and the small plant nursery behind a garden centre are all ancillary.

Subordination is about function rather than size alone, though size is strong evidence. A 200 m² storage area serving a 60 m² shop looks odd, and an officer will ask whether the shop is now serving the storage rather than the other way round.

Section 55 of the Town and Country Planning Act 1990 makes a material change of use development. Where an activity is ancillary, there has been no change of use at all, because the use of the planning unit remains what it was. That is why the planning unit, not the room, is the thing to identify first.

The planning unit and the primary use

The approach that practitioners still use comes from Burdle in 1977. Take the unit of occupation as the starting point. Where it has a single main purpose with other activities incidental to it, the whole is one planning unit. Where there are two or more physically distinct areas occupied for substantially different and unrelated purposes, each is a separate planning unit, whether or not they are in one ownership.

Three consequences follow for everyday advice.

The unit can be larger than the building, so a yard, a car park and a storage building can all form part of one unit with a workshop.

The unit can be smaller than the building, which is the point at issue in the note on upper floors above a shop as a separate planning unit. Flats above a shop in one ownership are usually a separate unit, which changes the analysis of everything else.

And identifying the unit wrongly at the start makes every later conclusion wrong, which is why the first paragraph of any advice note on this subject should state the unit and the primary use expressly.

Scale, independence and separate access

Five factors do most of the work when assessing whether an element has stopped being ancillary.

• Relative scale: floorspace, turnover, customer numbers and staff numbers compared with the primary use.
• Functional dependence: whether the element could operate if the primary use ceased tomorrow.
• Physical separation: its own entrance, its own frontage, its own signage, a wall between it and the rest.
• Commercial independence: separate opening hours, separate marketing, a separate rating assessment, its own till and its own staff.
• Customer profile: whether people come for the element rather than for the primary use.

A trade counter in a storage and distribution unit is the classic example. A counter serving existing customers collecting orders is ancillary. A counter with its own door, its own sign, retail opening hours and passing trade is a retail use, and the point is reached before anyone writes it down. The related change between storage and industrial use is covered in the note on general industrial to storage and distribution, and the amenity-based distinction within Class E is set out in the note on light industrial and office uses inside Class E(g).

When the ancillary element outgrows the main use

The phrase practitioners use is that the tail begins to wag the dog. The legal position is that a material change of use has occurred, and the test is whether the character of the use of the planning unit has changed as a matter of fact and degree.

Three patterns recur.

Growth without separation, where a farm shop selling the holding's produce starts buying in goods, extends its hours, advertises and draws customers from a wide area. The use becomes retail, and the fact that the farm still operates does not save it.

Separation without growth, where an ancillary element is physically divided off, let separately or sold, and becomes a distinct unit even though the activity has not expanded.

Intensification, where nothing about the description changes but the volume does. Intensification can amount to a material change where it alters the character of the use, and traffic generation, hours, noise and the number of visitors are the indicators officers reach for.

Honest advice to a client here is often uncomfortable. The answer is a matter of fact and degree, which means there is no threshold to design to, and a scheme that sits close to the line should be regularised rather than defended.

Conditions limiting the ancillary element

Where permission is being sought, the sensible course is to offer a condition rather than leave the extent of the ancillary element to be argued later.

Workable wording ties the element to the primary use and caps it. Four forms that work:

• The cafe shall be used only in conjunction with and ancillary to the garden centre and shall not be used as a separate unit.
• The retail floorspace shall not exceed the area hatched on the approved plan.
• The trade counter shall operate only during the hours stated.
• The ancillary office floorspace shall not exceed a stated proportion of the gross internal area.

Two drafting points. Reference a plan with the area hatched rather than a bare number, because a number without a location invites an argument about which space is counted. And avoid conditions that forbid the use being carried on independently without also capping the scale, because a small independent operation is easier to police than a large ancillary one.

Where the application also generates highway questions, a Transport Statement should describe the trips attributable to each element, because a transport case built only on the primary use undermines the argument that the other element is minor.

Evidence of the historic balance

Where a use is already established and the question is what the lawful use now is, the evidence is documentary and it should be assembled in the same way as for a certificate application.

1. Floor areas by activity, measured and plotted on a plan for each period.
2. Turnover split by activity from accounts, with the basis of apportionment stated.
3. Staff numbers and roles, from payroll records.
4. Opening hours over time, from advertising, signage photographs and website records.
5. Delivery and collection records, which show whether goods were moving as wholesale or retail volumes.
6. Rating assessments, which are third-party evidence of how the premises were described and valued.
7. Marketing material, which is often the most damaging document in the file because it describes the element as a destination in its own right.

A Planning Statement that sets out the planning unit, the primary use, the ancillary element and the balance over time, with those documents indexed behind it, is what an officer needs to agree a position rather than refer the file to enforcement.

Settling the position with a certificate

Where the answer carries commercial weight, the formal routes are a certificate of lawfulness of existing use or development under section 191, or of proposed use or development under section 192, of the Town and Country Planning Act 1990.

Use section 192 before making a change, because it answers whether the proposed arrangement would require permission, which is exactly the question a landlord, a funder or a purchaser asks. Use section 191 where the arrangement is already in place and has been for long enough to be immune, remembering that the relevant periods have been the subject of reform and should be checked against the current legislation.

A certificate is conclusive as to what it states and nothing more, so draft the wording carefully. It should describe the primary use, the ancillary element and the scale of it, because a certificate that simply names a use class leaves the ancillary question open for the next officer.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that a use is lawful.

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