Development: what section 55 actually means

The definition of development in planning is the gate everything else passes through. If what you are doing is not development, planning control does not apply to it, there is nothing to apply for and nothing to enforce against. If it is development, you need permission unless a development order has already granted it.

Section 55 of the Town and Country Planning Act 1990 supplies that definition, and it has two limbs.

The statutory definition

Development means 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.

Read that slowly, because the structure matters. The first limb is about operations, which are physical works. The second is about use, which is about what happens on the land rather than what is built on it. A single project can involve both, and they are assessed separately.

The distinction has practical consequences. Operational development is complete when the work is finished, and enforcement time limits run from then. A change of use is a continuing state of affairs, and the analysis of when it began is a question of evidence.

Operations: building, engineering, mining and other

Building operations are defined in the Act to include demolition of buildings, rebuilding, structural alterations of or additions to buildings, and other operations normally undertaken by a person carrying on business as a builder. That final phrase is the catch-all, and it is why laying foundations, erecting a structure or forming an opening in a wall are all operations even where none of them is obviously "building" in ordinary speech.

Engineering operations covers earthworks, the formation of accesses, hard standings, retaining structures and level changes. It is the limb that catches the things people assume are outside planning because nothing has been built: regrading a paddock, excavating for a court, forming a bund.

Mining operations covers the winning and working of minerals, including on a small scale.

"Other operations" is read in the light of the three named categories rather than as an open door, but it is not empty, and courts have used it where a physical change to land does not sit comfortably in the other three.

One provision is worth knowing on its own. Works to alter a building by providing additional space underneath the ground are development, even though they might otherwise be excluded as internal works. Basement excavation is development.

Material change of use

The second limb has two words doing the work: material, and change.

Change means a shift in the character of the use, not a change of occupier, ownership or trading name. A shop that changes hands is not development. A shop that becomes a hot food takeaway is.

Material is a question of fact and degree, judged on the planning consequences. The test is not whether something is different but whether the difference matters in planning terms: traffic, noise, hours, odour, refuse, character of the area, effect on neighbours. Doing more of the same thing can cross the line, and the question of when intensification becomes development is one of the recurring arguments in enforcement.

Two things have to be settled before the question can be answered. What is the lawful use you are comparing against, and what is the planning unit you are assessing. Getting the unit wrong produces the wrong answer, because a change confined to part of a larger unit may be immaterial at the level of the whole.

The Act also deems certain changes to be material. The use as two or more separate dwellings of a building previously used as a single dwelling is one, which is why splitting a house into flats is always development regardless of whether any building work is involved.

What section 55 expressly excludes

The Act lists things that are not development, and this is the part householders should know:

• works of maintenance, improvement or other alteration to a building that affect only the interior, or that do not materially affect the external appearance, subject to the basement provision above
• works by a highway authority to maintain or improve a road, carried out within the boundaries of the road
• works by a local authority or statutory undertaker to inspect, repair or renew sewers, mains, pipes, cables and other apparatus, including breaking open a street
• the use of any building or other land within the curtilage of a dwellinghouse for any purpose incidental to the enjoyment of the dwellinghouse as such
• the use of land for agriculture or forestry, and the use for those purposes of any building occupied with land so used
• a change of use within the same class specified in the Use Classes Order

The last two are the ones that get stretched. Agricultural use is exempted, but erecting a building for agriculture is an operation and remains development, permitted or not. And movement within a use class is only free where the new use falls squarely within the same class, which after the 2020 restructuring of the Order is not always obvious.

The interior works exemption is narrower than it sounds too. Internal alterations that enable a change of use are not saved by it, because the change of use is the development, not the alterations.

Why de minimis matters in enforcement disputes

The courts have accepted that some works and some changes are too trivial to amount to development at all. There is no threshold written into the Act, and the principle is applied sparingly.

Where it does bite is in enforcement arguments, where a council alleges a breach and the recipient says the difference is negligible. Replacing a window with an identical window. Painting a wall that is not in a conservation area and not listed. Parking a single trailer on a drive. These are the sorts of facts where the argument runs.

Do not build a project on de minimis. It is a defence at the margin, not a planning strategy, and the burden of establishing it sits with the person relying on it.

Where to check if you are unsure

Three routes, in increasing order of certainty.

Ask the council's duty planner or use its pre-application service. Quick and useful, and the answer is informal advice that does not bind the authority.

Take advice from a planning consultant, which gets you a reasoned view and, where the position is arguable, a strategy.

Apply for a Lawful Development Certificate. Under section 192 of the Act you can ask the council to certify that a proposed use or operation would be lawful, and under section 191 that an existing one already is. This is the only formal way to confirm that works are lawful. The proposed version costs half the fee of the equivalent planning application, produces a decision with a right of appeal, and cannot be revoked unless it was obtained by concealing or misrepresenting the facts.

For anything where the answer changes what you spend, the certificate is the least expensive option, whatever it costs.

This is general guidance, not legal advice. Whether something amounts to development turns on the facts of each case. Check the position with your local planning authority or a qualified professional before relying on it.

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