Core principles of planning law - Statutory definition of 'd...

Learning Outcomes

This article explains the statutory definition of 'development' in planning law, including:

• Applying section 55 TCPA 1990 to identify when proposals involve operational development or a material change of use
• Distinguishing activities that fall within and outside the definition of 'development', with reference to statutory language and key exclusions
• Analysing factual planning scenarios and advising confidently on when planning permission is needed
• Differentiating operational development from material change of use and recognising the importance of the planning unit and ancillary/incidental uses
• Evaluating whether intensification of an existing use has crossed the line into a material change in planning terms
• Using the Use Classes Order to determine whether a change is not development because it falls within a single use class
• Applying the GPDO to identify when development has deemed planning permission and when Article 4 directions withdraw those rights
• Deploying lawful development certificates to de‑risk borderline proposals and to secure certainty over existing or proposed uses and operations

SQE2 Syllabus

For SQE2, you are required to understand the statutory definition of 'development' in planning law, including operational development, material change of use, key exclusions, and the interplay with the Use Classes Order and GPDO, and to apply these principles to client-based scenarios, with a focus on the following syllabus points:

• The statutory definition of 'development' in section 55(1) Town and Country Planning Act 1990.
• The types of activity included as operational development and material changes of use.
• Activities expressly excluded from the definition of 'development' and their relevance.
• How to apply the definition to practical, client-based planning scenarios.
• The effect of section 55(1A) TCPA 1990 (operations “normally undertaken by a person carrying on business as a builder”).
• The relationship between section 55 and the Town and Country Planning (Use Classes) Order 1987, as amended.
• The role of the Town and Country Planning (General Permitted Development) Order 2015 (GPDO), including Article 4 directions that can withdraw permitted development rights.
• Concepts of planning unit, primary/ancillary uses, and incidental residential uses.
• Lawful Development Certificates for proposed and existing uses/operations (sections 191–192 TCPA 1990).

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.

1. Which statute and section provide the definition of 'development' for planning purposes?
2. True or false? Altering the interior layout of a house always constitutes 'development'.
3. Give an example of an activity specifically excluded from the statutory definition of 'development'.
4. Why is the statutory definition of 'development' essential for advising on planning permission?

Introduction

The planning system in England and Wales regulates land use and development in the public interest. At the core of planning control is the concept of 'development.' Identifying what counts as 'development,' as defined by statute, is the first step in determining whether planning permission is required for any activity affecting land or buildings. The requirement for planning permission flows from section 57(1) TCPA 1990, which provides that planning permission is required for the carrying out of any development of land. For SQE2, you must be able to interpret the statutory definition, recognise key exclusions, understand the interplay with the Use Classes Order and the GPDO, and apply the law to real-world client instructions.

The Statutory Definition of 'Development'

The starting point for planning law is the statutory definition found in section 55(1) of the Town and Country Planning Act 1990 (TCPA 1990):

Key Term: development
The legal meaning of 'development' is "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." This definition has two main components:

1. Operational development: Most physical works to land—such as erecting, extending, demolishing, engineering, mining, or rebuilding.
2. Material change of use: Significant changes to the way land or buildings are used, usually where the use falls into a different statutory use class.

Section 55(1A) adds that “building operations” include operations normally undertaken by a person carrying on business as a builder, which helps capture a wide range of physical works (e.g. structural alterations, new foundations, major earthworks).

Key Term: operational development
The carrying out of construction, demolition, engineering, mining, or similar physical works in relation to land.

Key Term: material change of use
A change in how land or buildings are used that is significant in planning terms, often triggering a different use class under planning law.

Although the statutory words appear simple, they contain several important judgments:

• Whether works are “operations” and whether they are de minimis (trifling).
• Whether a change in use is “material”, which is a fact-and-degree assessment.
• Whether a change occurs at the level of the relevant “planning unit”.

Key Term: planning unit
The area of land within which a single, primary use is to be identified, and where any ancillary uses are ordinarily regarded as part of that primary use.

Key Term: ancillary use
A use that is ordinarily incidental or subordinate to a primary use and is part and parcel of it. An ancillary use does not usually constitute a separate planning use.

Application: Examples of 'Development'

• Building a new residential extension.
• Converting a field into a car park (engineering operations and material change of use).
• Demolishing a building in preparation for a new use (demolition is an operation, often controlled through GPDO prior approval).
• Changing the primary use of a shop to a restaurant (if the relevant use classes differ).
• Subdividing a single dwellinghouse into two separate self‑contained flats (material change of use creating an additional dwelling).
• Constructing a raised terrace, significant retaining wall, or bund (engineering operations).
• Erecting a fence over height thresholds (a building operation; often permitted under the GPDO within limits).

Activities Excluded from 'Development'

Not all works or changes relating to land are classed as 'development.' Section 55(2) TCPA 1990, as supplemented by statutory instruments, excludes certain activities from the definition. The most frequently encountered are:

• Internal works: Alterations affecting only the interior of a building that do not materially affect its external appearance (s55(2)(a)). This does not extend to creating new self‑contained dwellings within a building, which is a change of use, and there are special rules for large retail mezzanine floors (see below).
• Incidental curtilage uses: Use of buildings or other land within the curtilage of a dwellinghouse for purposes incidental to the enjoyment of the dwellinghouse as such (s55(2)(d)), e.g. a domestic garden building used for hobbies or storage.
• Changes within one use class: Switching between uses that fall within the same use class under the Town and Country Planning (Use Classes) Order 1987 (UCO) (s55(2)(f)).
• Use of land for agriculture or forestry: The use of land (as opposed to operational works) for agriculture or forestry is not development (s55(2)(e)). Many operational works to support these uses are permitted development, but substantial new buildings still require either permitted development cover or express permission.
• Routine repairs and maintenance: Works that do not materially affect the external appearance of the building will not amount to development under s55(2)(a).

Key Term: curtilage
The land immediately surrounding a dwelling, considered to be part of the property—such as gardens, driveways, or attached garages.

Key Term: Use Classes Order
A separate statutory instrument grouping uses of land and buildings into classes. Changes within a single class are not development, while changes between classes typically are (unless the GPDO grants permitted development rights).

Key Term: permitted development
Categories of minor development which have automatic deemed planning permission by law, so do not need express consent.

Key Term: Article 4 direction
A direction made by a local planning authority (or the Secretary of State) to remove specified permitted development rights in a defined area, so that planning permission is required.

Key Term: lawful development certificate
A formal certificate under sections 191–192 TCPA 1990 confirming that an existing or proposed use/operation is lawful (either because it is not development, is permitted development, or is immune from enforcement).

Use Classes: key points as at 2025

In 2020, major reforms introduced Class E (commercial, business and service) and new Classes F1/F2 (learning and non-residential institutions; local community). Many former A and B1 uses moved into Class E. By contrast, certain uses are “sui generis” (in a class of their own), such as pubs, hot food takeaways, cinemas, and large HMOs. Changes within Class E do not amount to development; however, moving to or from a sui generis use is normally a material change of use requiring permission unless a relevant GPDO right applies.

The GPDO also grants permitted changes of use subject to conditions and “prior approval” (e.g. Class MA: Class E to C3 dwellinghouses), but that is a question of permission, not whether the proposal is “development”.

Internal works and retail mezzanine floors

While internal works are typically excluded, an increase in retail floorspace by a new mezzanine above certain thresholds will constitute development and may require permission. The precise trigger depends on the specific regulatory provisions in force and any local limitations. Always check whether the proposal exceeds the relevant floorspace limit.

Planning unit, ancillary and incidental uses

Whether a change of use is material often depends on how the “planning unit” is used in the round and whether an additional, separate primary use has emerged. Ancillary or incidental uses form part and parcel of the main use and ordinarily do not amount to a material change. By contrast, introducing a new primary use or intensifying an ancillary activity to the point it changes the character of the use can amount to a material change.

Key Term: article 4 direction
A direction under Article 4 of the GPDO that withdraws specific permitted development rights in a defined area. These are common in conservation areas or where changes of use (e.g. Class E to C3) require tighter control.

Worked Example 1.1

A client proposes to reconfigure the internal non-structural walls of his house, creating an open-plan kitchen-diner, with no changes visible from outside. Is planning permission needed?

Answer:
No. If the works do not materially affect the external appearance, they are excluded from the definition of 'development.' Planning permission will not be required.

Worked Example 1.2

A small shop intends to convert to an estate agent's office, both of which fall within the same use class at the relevant time. Does the client need to apply for planning permission?

Answer:
No. Where the uses are in the same use class under the Use Classes Order, this change is not a material change of use, so does not constitute development. No planning permission is needed.

Worked Example 1.3

A residential property owner plans to build a wooden summer house at the end of their garden, used only for domestic hobbies. Is this 'development'?

Answer:
Using a building or land within the curtilage for purposes incidental to the enjoyment of the dwellinghouse is excluded from the definition of development, provided size and use limitations are not exceeded and the use remains ancillary.

Worked Example 1.4

A homeowner works from a spare room as a sole trader, occasionally meeting one or two clients at home during the week. Neighbours complain and ask if this is a “material change of use.”

Answer:
Homeworking that remains ancillary to the residential use typically does not amount to a material change. If activity, traffic or disturbance grows so that the character of use becomes partly commercial in its own right (e.g. regular client footfall, employees, signage), it can cross the line into a material change of use. Fact and degree.

Worked Example 1.5

A landlord converts a 3‑bed house (C3) to a small HMO for five occupants (C4). Is this development?

Answer:
Yes, it is a change between use classes (from C3 to C4) and therefore a material change of use. However, the GPDO grants permitted development rights for some C3↔C4 changes, commonly subject to conditions and Article 4 directions. If an Article 4 direction applies, express permission will be needed.

Worked Example 1.6

A retailer installs a new mezzanine floor increasing the shop’s retail floorspace by over the specified threshold. The works are entirely internal. Is planning permission required?

Answer:
Yes. Large mezzanine floors in retail premises can fall outside the internal works exclusion and constitute development. Floorspace thresholds apply; if exceeded, permission is required.

Worked Example 1.7

A farmer wishes to start using existing pasture for grazing sheep. Are they undertaking development?

Answer:
No. Using land for agriculture is not development (s55(2)(e)). New buildings or substantial engineering works may still be development, though many agricultural operations benefit from permitted development rights under the GPDO, typically with prior approval.

Worked Example 1.8

A single dwellinghouse is reconfigured internally to create two self‑contained flats with separate entrances but no external works. Development?

Answer:
Yes. Even if the works are internal, creating an additional dwelling is a material change of use. Planning permission is required unless a relevant permitted development right applies (which is rare for such subdivision).

Material Change of Use: fact and degree

Whether a change is “material” is a question of planning judgment. Consider:

• The character of the activities and their planning impacts (traffic, noise, hours, visitors).
• Whether the new use is in a different use class (usually material unless the GPDO grants a permitted change).
• Whether the new activity is ancillary/incidental to the primary use (usually not material) or has become a separate primary use (likely material).
• Whether intensification alters the character of the use in a material way.

Key Term: Use Classes Order
The Town and Country Planning (Use Classes) Order 1987 (as amended) groups uses. Important modern classes include C (residential), E (commercial, business and service), F1/F2 (learning/community). Certain uses (e.g. pubs, takeaways, large HMOs, cinemas) are sui generis.

Since September 2020, many former retail, café and office uses are within Class E. Moving between those sub‑categories is not development; however, moving to a residential (C3) use is normally a material change unless a GPDO route (e.g. Class MA) is used and prior approval obtained.

Demolition

Demolition is an operation and therefore development. The GPDO provides a route for certain demolitions subject to prior approval (and separate listed building/conservation area consent regimes may apply). Always check whether conservation area controls, listed building status, or Article 4 directions affect the position.

Engineering and other operations

Raising ground levels, creating hardstandings of significant scale, forming new access tracks, constructing retaining walls or bunds, and major drainage works are usually engineering operations and development. Some smaller operations may be permitted development (e.g. domestic hardstanding within limits), but that concerns permission, not the definitional question.

Why the Definition Matters

Establishing whether a proposal constitutes 'development' is fundamental in practice. Only development requires planning permission (unless permitted development applies). If an activity or work is not classed as 'development,' planning control does not apply, and no planning permission is needed. Conversely, if a proposal is development, you must then ask whether it benefits from permitted development rights (often with conditions and prior approval) or whether express permission is required.

It is a criminal offence to carry out development without the necessary planning consent. Advising correctly on whether a proposal is development is therefore a key step before any work or change of use is begun.

Where a proposal is borderline (e.g. ancillary/incidental, intensification, or internal works near the mezzanine thresholds), consider a Lawful Development Certificate to obtain certainty in advance (s192 for proposed; s191 for existing). If development has occurred without permission, enforcement powers and time limits (commonly 4 years for operational development and 10 years for changes of use and breach of condition, subject to exceptions for concealment) become relevant, but those are separate from the definitional step.

Exam Warning

Always check the exclusions carefully—internal alterations and changes within the same use class are frequent sources of error in exams and practice. Use classes and specific interpretations change periodically through revised statutory instruments. For material change of use questions, identify the relevant planning unit and whether the new activity is ancillary or has become a separate primary use. Remember that large retail mezzanines can be development even if works are internal.

Key Point Checklist

This article has covered the following key knowledge points:

• The planning system applies only to activities falling within the statutory definition of 'development.'
• Operational development includes most construction, demolition, and significant physical works; section 55(1A) extends this to operations normally undertaken by builders.
• Material changes of use, if significant in planning terms, are also development; the test is one of fact and degree at the level of the planning unit.
• Section 55(2) sets out explicit exclusions from 'development,' including interior alterations not affecting external appearance, certain uses incidental to the enjoyment of a dwellinghouse, agriculture/forestry use of land, and changes within one use class.
• The Use Classes Order groups uses: changes within a single class are not development; changes to or from sui generis uses generally are development.
• The GPDO grants permitted development rights for many operational works and some changes of use (often subject to prior approval); Article 4 directions can withdraw those rights.
• Internal retail mezzanine floors above specified limits constitute development notwithstanding the general internal works exclusion.
• Where in doubt, a Lawful Development Certificate can provide certainty for proposed or existing activities.

Key Terms and Concepts

• development
• operational development
• material change of use
• planning unit
• ancillary use
• curtilage
• Use Classes Order
• permitted development
• article 4 direction
• lawful development certificate