Section 55 and when a change of use is not development

Section 55 of the Town and Country Planning Act 1990 defines development as the carrying out of building, engineering, mining or other operations in, on, over or under land, or the making of any material change in the use of any buildings or other land. Everything in development management flows from that sentence. If a proposal is not development, no permission is needed, no fee is payable and the council has no jurisdiction, whatever an officer says on the telephone.

The material change of use limb is where the arguments live. Section 55 does not define material, and no statutory instrument has ever supplied a threshold. The courts have consistently treated it as a question of fact and degree for the decision maker, which means an inspector can reach a different answer on facts a case officer thought obvious.

The exclusions in subsection 2 do most of the work

Section 55(2) lists matters that are not to be taken as involving development. Four of them come up constantly.

Works of maintenance, improvement or other alteration affecting only the interior of a building, or not materially affecting its external appearance, are excluded by subsection 2(a). That is the internal works exclusion, and it is about operations rather than use.

Use of buildings or other land within the curtilage of a dwellinghouse for any purpose incidental to the enjoyment of the dwellinghouse as such is excluded by subsection 2(d). Incidental is doing a lot of work in that phrase. A home gym in an outbuilding is incidental. A commercial dog grooming business run from the same outbuilding is not.

Use of land for agriculture or forestry, and use for those purposes of any building occupied with agricultural land, is excluded by subsection 2(e). The exclusion covers the use, never the buildings that agriculture might need, which is why agricultural buildings sit under Part 6 of the General Permitted Development Order instead.

Subsection 2(f) is the one that makes the Use Classes Order function. Where a building or land is used for a purpose of a class specified in that order, use for any other purpose of the same class is not development. Since September 2020 that class has included the very broad Class E, which absorbed shops, financial and professional services, cafes and restaurants, offices, light industry, clinics, gyms, nurseries and indoor sport in one place.

Fact and degree, and how officers actually apply it

Materiality is judged in planning terms, so the question is whether the change has planning consequences of a kind and scale that ought to be controlled. Character matters more than label. A change that leaves the pattern of comings and goings, servicing, hours, noise and neighbour effects broadly as before is unlikely to be material, even if the trading name over the door has changed entirely.

Officers look at a familiar set of indicators. Trip generation and parking demand. Hours of operation, including deliveries. Noise, odour and extraction. Whether the use draws the public into a building that previously had none. Waste volumes and storage. The number of separate occupations within one building.

Intensification sits inside this analysis rather than beside it. A use can grow until its character changes, and at that point it has become a different use. The line is not a percentage. It is the moment when the planning consequences differ in kind.

The planning unit is chosen before the question is answered

A change of use is assessed against a unit of land, and identifying that unit comes first. The conventional starting point is the whole of a single occupier's holding where there is one main use, with any other activities ancillary to it. Where two or more physically separate areas are in separate uses in fact, each can be its own unit.

The consequence is practical. A farm shop occupying a corner of a large agricultural holding may be ancillary to the farm and no change of use at all. The same shop, once the holding is split and the shop sits on its own title with its own access and car park, is a separate planning unit in retail use, and the change happened when the separation did.

Getting the unit wrong produces the wrong answer with perfect logic. Objectors regularly argue for a small unit, because a small unit makes any new activity look dominant. Applicants argue for a large one. The council decides, and an inspector can decide differently on appeal.

Three questions settle most disputes. Is there a single main use to which everything else on the site is subordinate. Are the physically separate parts occupied by the same person for the same purpose. Has anything happened, a sale, a lease, a fence, a separate access, that broke the holding into pieces. Answer those in the application and the officer has less room to reframe the site to suit an objection.

What subsection 3 puts beyond argument

Section 55(3) removes two questions from the fact and degree exercise. The use as two or more separate dwellinghouses of any building previously used as a single dwellinghouse involves a material change of use of the building and of each part. That is why converting a house into two flats always needs permission, however modest the works.

Depositing refuse or waste on land already used for that purpose is also treated as a material change where the height of the deposit is raised above the level of the adjoining land or the area of the deposit is extended. Both provisions exist because the general test produced unhelpful arguments.

The subdivision rule has a corollary that catches landlords. A house in multiple occupation is not a set of separate dwellinghouses, because the occupiers share facilities and the building remains one unit. Moving from Class C3 to Class C4 is a change between classes rather than a subdivision, and in most of England it is permitted development under Part 3 unless an article 4 direction has removed the right. Splitting the same house into self-contained flats with their own kitchens and bathrooms is subsection 3 territory and always needs permission.

Where the conclusion is confirmed

An informed view that no permission is needed is worth exactly what it is written on until it is certified. Section 191 provides for a certificate of lawfulness of an existing use or development, and section 192 for a proposed one. The section 192 route is the sensible course before spending money on a fit-out, and lenders and buyers increasingly ask for it.

Illustrative example: a former bank in Class E is taken by a physiotherapy practice with two treatment rooms and reception. Same class, so section 55(2)(f) applies and no permission is needed. The practice later adds evening pilates classes for twenty people, twice a week, with amplified music. Indoor sport is also within Class E, and the character question then turns on hours, noise and parking rather than on the class label. This example is illustrative.

Where the answer is borderline, put the reasoning in writing and support it. A short planning statement that sets out the planning unit, the use history and the character comparison is the document an officer can agree with or attack, and either is better than silence. Add a transport statement where trip generation is the disputed point, or a ventilation and extraction statement where cooking is involved.

PlanScope drafts those documents structured to UK planning policy and flags the site facts that need confirming. Enter your postcode on the PlanScope home page to see which reports a change of use 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.