Prior Approval in London: When You Need It, When You Do Not, and How the Process Works

Prior Approval is a planning consent mechanism that sits between full planning permission and straightforward permitted development. It allows certain types of development to proceed without a full planning application, while still giving the local planning authority (LPA) an opportunity to assess specific aspects of the proposal before work begins.

Unlike full permitted development rights — where you simply carry out the work and take responsibility for compliance — Prior Approval requires you to formally notify the LPA of your intended development. The LPA then has a set period (usually 42 days) to determine whether Prior Approval is required for certain specified matters and, if so, whether those matters meet the relevant conditions.

For London homeowners, the most commonly encountered Prior Approval route is the Larger Home Extension scheme, formally known as Class A of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015.

The Larger Home Extension scheme allows householders to construct single-storey rear extensions that are larger than the standard permitted development limits but within certain maximum dimensions, without full planning permission.

Under standard permitted development rights for single-storey rear extensions:

• Detached houses may extend up to 4 metres from the rear wall
• Terraced and semi-detached houses may extend up to 3 metres from the rear wall

Under the Larger Home Extension Prior Approval scheme:

• Detached houses may extend up to 8 metres from the rear wall
• Terraced and semi-detached houses may extend up to 6 metres from the rear wall

This is subject to the extension not exceeding 4 metres in height, not being within 2 metres of a boundary if over 4 metres high, and other standard permitted development conditions applying (materials, not exceeding half the garden area, and so on).

For many London homeowners with terraced houses, the Prior Approval route allows an extension of up to 6 metres rather than 3 metres — a significant difference in usable space, achieved without the cost, time, and uncertainty of a full planning application.

The Prior Approval process for the Larger Home Extension scheme involves a neighbour consultation procedure:

Step 1 — Submit a Prior Approval application to the LPA. This typically requires a completed form, a site location plan, a block plan showing the proposed extension relative to the property and its neighbours, details of the proposal (dimensions, materials, elevation drawings), and the application fee (currently £120 as of 2025).

Step 2 — Neighbour notification. The LPA notifies the owner and occupiers of adjoining properties about the proposed extension. Adjoining properties include those sharing a boundary with the application site — typically the neighbours on each side and any property directly behind the rear boundary.

Step 3 — Representation period. Adjoining neighbours have 21 days from notification to make representations. If no representations are received, the LPA must issue a Prior Approval Not Required notice and the extension may proceed.

Step 4 — Assessment if representations received. If neighbours object, the LPA must consider the impact of the proposed extension on the amenity of adjoining properties (primarily in terms of light, outlook, privacy, and overshadowing). The LPA cannot refuse on general design or planning policy grounds — only on the impact on neighbouring amenity.

Step 5 — Decision. The LPA either grants Prior Approval (possibly with conditions), refuses Prior Approval, or determines that Prior Approval is not required. If a decision is not issued within 42 days, the development may proceed as if Prior Approval was not required.

Even where Prior Approval is not required or is granted, the development must still comply with all the conditions of the permitted development right, including:

• The extension must be at the rear of the house
• Maximum height restrictions (4 metres for single-storey)
• The extension must not extend beyond a side elevation of the original house
• Materials should be similar in appearance to existing materials (though this is a condition to demonstrate compliance, not a Prior Approval matter)
• The development must not result in the total area of structures within the curtilage exceeding 50% of the total area of the curtilage

If your proposal does not meet all conditions of the permitted development right, Prior Approval is not the route — full planning permission will be needed regardless of extension size.

Beyond the Larger Home Extension scheme, Prior Approval is also required for certain other development types relevant to London homeowners:

Change of use — Class MA (commercial to residential) — converting commercial, business, and service buildings to residential use requires Prior Approval, allowing the LPA to assess transport impacts, flooding risk, contamination, and noise before conversion proceeds.

Telecommunications — mobile phone masts and ancillary apparatus require Prior Approval assessment for their visual impact and structural method.

Agricultural buildings to dwellinghouses — conversion of agricultural buildings to residential use under Class Q permitted development requires Prior Approval.

Extensions to schools and colleges — certain enlargements of educational premises require Prior Approval.

Solar panels and ground source heat pumps — certain renewable energy installations require Prior Approval assessment.

For householder developments, the Larger Home Extension scheme is by far the most commonly used Prior Approval route in London.

Article 4 Directions remove or modify permitted development rights in designated areas. In London, Article 4 Directions are common in conservation areas and some residential areas where local planning authorities consider it important to control the character and appearance of the area.

If an Article 4 Direction removes the permitted development rights that underpin the Larger Home Extension Prior Approval scheme, full planning permission will be required even for extensions that would otherwise fall within the scheme's dimensions.

Always check whether Article 4 Directions apply to your property before assuming the Prior Approval route is available. Your local planning authority's website will list current Article 4 Directions, or you can check with a planning consultant.

Some householder projects use Prior Approval for the extension itself while addressing other works through Lawful Development Certificates or full planning permission. For example:

• A rear extension under the Larger Home Extension scheme may be combined with a loft conversion under standard permitted development (no Prior Approval required for standard dormer lofts within PD limits)
• A garage conversion under Class A permitted development may be combined with a rear extension under Prior Approval

Sequencing applications to use the most efficient consent route for each element of a project can save time and cost overall.

rcbGroup has experience assisting London homeowners understand which planning consent route is most appropriate for their project and coordinating the preparation of Prior Approval applications where needed.

Our pre-construction process includes reviewing the planning position for each project — identifying permitted development potential, Article 4 restrictions, and the most efficient path to consent. Where Prior Approval is the right route, we work with architects and planning consultants to ensure applications are properly prepared and submitted.

Speak to us at the earliest stage of your project to understand your options before investing in design work for a project that may require a different planning approach than you expected.