Whether because you want to extend your home, start a small business, or deal with something a neighbour has built — you’ve probably heard the word “development” thrown around a lot. It’s one of those terms that sounds straightforward… until you actually try to pin down what it means.

In the planning system, development has a specific legal definition set out in Section 55 of the Town and Country Planning Act 1990. You don’t need to memorise legislation to understand it — but knowing the basics can save you time, money, and in some cases, enforcement trouble.

So, what is “development”?

Section 55 tells us there are two main types of things that count as development:

1. Physical works — doing something to the land

This includes building things, engineering works, digging, mining, or pretty much any operation that physically changes land or buildings.

Think of:

• Building an extension

• Laying new foundations

• Erecting a fence over a certain height

• Excavating a basement

• Creating a hardstanding

• Digging out a lake or reservoir

• Putting up a new outbuilding

These are all physical changes. The law sometimes calls this “operational development”.

A helpful way to think about it is: Have you permanently changed the land or the structure of something? If yes, it’s likely development.

2. Changing how land or buildings are used

This is called a material change of use. It isn’t about physically altering anything; it’s about what happens on the land.

Common examples:

• Turning a shop into a café

• Renting a house as a holiday let instead of a family home

• Converting a garage into a home office (sometimes)

• Using farmland as a caravan site

• Turning a field into a parking lot

Even if you haven’t touched a brick, switching to a different use category can count as development in the planning world.

Why does this matter?

Because if something is development, then normally you must have planning permission before doing it.

If you don’t, the council can take enforcement action, and that’s rarely fun.

So before you build, dig, move, or repurpose anything, it helps to understand which category your idea falls into.

Not everything is development

Section 55 also gives a list of things that aren’t considered development at all. These tend to be:

• Very small physical changes

• Certain interior works

• Some changes within the same use class

• Temporary uses

• Agricultural activities

So just because you’re doing something, it doesn’t automatically mean you need planning permission.

But sometimes the line is blurry

Here’s where things get interesting — and confusing — for homeowners, landowners, and small businesses alike.

Some activities include a bit of building, a bit of new use, and maybe even a bit of engineering. In these cases, professionals and inspectors often need to work out what the dominant part of the activity is.

Let’s unpack a few real-world scenarios to show how this plays out.

Scenarios Where People Need to Understand “Development”

1. “I’m creating a pond — do I need permission?”

You might think making a pond is just gardening. But if it involves earthworks, reshaping the land, or altering drainage, it might count as engineering operations — which are a form of development.

In some cases, building a reservoir also involved extracting gravel. Because the gravel removal was significant in its own right (not just an incidental side-effect), both activities could be treated as development requiring planning permission.

Takeaway: Even “natural” features like ponds or lakes can be development if they physically reshape land.

2. “I’m tipping soil or rubble — is that a use or an operation?”

Imagine someone is bringing in lorry loads of soil and spreading it over land. Are they:

• levelling the site as part of an engineering operation (an operational development), or

• using the land as a waste disposal site (a material change of use)?

Both possibilities exist, depending on the ultimate purpose.

Takeaway: Activities with multiple possible explanations may require professional judgement.

3. “I’ve got a floating structure — does that count as development?”

A prefabricated structure anchored to the bank of a river and used as a residence, could be considered a houseboat, and thus part of the land for planning purposes.

Why does that matter? Because if something is considered land, changing it can be development.

Takeaway: If it’s permanently attached and functions like a building, even a floating structure might fall under planning control.

5. “I’m only doing a small part of the work — is that separate development?”

Sometimes you have composite activities — different actions happening as part of the same project. The key question is: Is one activity just a by-product of another, or are they both major elements?

If two substantial activities are happening together, each may require planning permission.

Takeaway: A project with multiple components can trigger more than one type of development.

When should you stop and ask?

Understanding whether YOUR project counts as development can save you from major headaches. Here are everyday situations where it’s wise to pause and consider:

✔ Building or extending anything

Even temporary-looking structures can be “operational development” if they’re fixed in place.

✔ Changing what you use a building or land for

Holiday let conversions, outdoor events spaces, new business uses — these often trigger material change of use rules.

✔ Landscaping works

Earth movement, new access points, large patios, or ground-level changes might count.

✔ Anything involving water

Marinas, houseboats, moorings, floating structures, or operational facilities on water can involve the use of the riverbed.

✔ Projects with multiple parts

If your project has excavation, construction, and a new land use all wrapped into one, each piece might be treated separately.

Final thoughts: Development is broader than most people expect

A lot of people imagine development is just building things — bricks and mortar. But as you can see, the planning definition is much wider. It covers physical works, changes in how land is used, and sometimes even activities that happen on or above water.

If you’re unsure whether something is development, or how it might be classified, it’s always worth checking early. A short conversation with a planning professional can prevent months of stress later on.

And for anyone dealing with neighbours’ structures, odd new activities on nearby land, or their own renovation dreams, understanding the basics of Section 55 gives you a powerful head-start.

About Me

Andrew Ransome is the planning director at ADP and is a chartered member of the RTPI, with over 22 years of town planning experience.

Andrew has extensive experience offering strategic planning solutions to challenging projects in both rural and urban settings. Follow him on Linkedin.

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