How Long Does Planning Permission Last in London? 2026 Guide for Homeowners

You have received planning permission for your extension, loft conversion or renovation, but construction is not ready to start.

How much time do you actually have?

For most planning permissions in England, the starting point is three years from the date permission is granted to begin the development. That does not normally mean the project has to be finished within three years.

However, the three-year rule should never be used without reading your actual decision notice. Under Section 91 of the Town and Country Planning Act 1990, a local planning authority normally imposes a commencement condition requiring development to start within three years, but it can specify a shorter or longer period where appropriate. The deadline written into the permission therefore takes priority over a generic online rule.

The current GOV.UK guidance on planning conditions confirms that the normal period is three years from the date permission is granted, unless the local planning authority imposes another period.

For London homeowners, this means the first document to check is not an article, an architect’s email or the Planning Portal submission date. It is your planning decision notice and its conditions.

Last reviewed: August 2026. This article relates primarily to planning law in England. Different systems and timescales apply elsewhere in the UK.

At a Glance: How Long Does Planning Permission Last in 2026?

The details behind those answers matter, particularly when a permission is approaching expiry.

How Long Does Full Planning Permission Last?

For most detailed planning permissions, development must normally begin within three years from the date permission is granted. This is established through the commencement condition attached to the planning permission.
For example, if a decision notice states:

“The development hereby permitted shall be begun before the expiration of three years from the date of this permission.” you need a lawful commencement before that period expires.

Do not calculate the deadline from the day you submitted the planning application, the validation date, the date a planning committee discussed it or the day you happened to open the decision email.

Check the date on which the permission was actually granted and the wording of the commencement condition.

GOV.UK confirms that the local authority may impose a period shorter or longer than three years in appropriate circumstances, so your individual decision notice is authoritative for your project. Read the official planning-condition guidance.

Three Years to Start Does Not Mean Three Years to Finish

This distinction causes a great deal of confusion. The usual three-year planning condition relates to commencement, not completion.

Once a planning permission has been lawfully implemented in time, the permission does not ordinarily expire simply because construction continues beyond the original three-year date.

That does not give a homeowner unlimited freedom to build however they wish. The development still needs to follow the approved permission and its conditions. Building Regulations, Party Wall requirements and other applicable controls also remain separate.

The important issue is whether the development was lawfully commenced before the planning permission’s implementation deadline.

What Counts as Starting Work on a Planning Permission?

Planning law uses the concept of beginning development through a material operation. Section 56 of the Town and Country Planning Act 1990 identifies operations that can constitute commencement, including relevant construction work, digging a foundation trench, certain underground works serving foundations, road construction and, where part of the development, demolition.

You can read the statutory provision directly in Section 56 of the Town and Country Planning Act 1990. But simply carrying out some physical work does not automatically protect the planning permission.

The work needs to genuinely implement the approved development. If your approved extension is in one position but a trench is excavated somewhere else on the site, you should not assume the permission has been commenced.

Likewise, temporary fencing, site clearance or a survey should not be relied upon as commencement simply because somebody has attended the property.

Does Digging a Foundation Trench Keep Planning Permission Alive?

A genuine foundation trench can constitute a material operation when it forms part of the approved development. But the commonly repeated advice to “dig one trench before the permission expires” is too simplistic.

The work needs to relate to the permission you are implementing. The approved plans, dimensions, location and any relevant conditions all matter.

Before carrying out commencement works solely to preserve a planning permission, have the proposed operation reviewed against the actual permission.

This becomes especially important when the site has pre-commencement planning conditions.

Check Pre-Commencement Conditions Before You Start

Starting physical work is not the only consideration. Some permissions contain conditions requiring particular information to be approved before development commences.

These can relate to matters such as construction management, trees, materials, contamination, drainage or other project-specific issues.

GOV.UK explains that development undertaken without complying with a valid pre-commencement condition can be unlawful and may be subject to enforcement. See GOV.UK’s guidance on pre-commencement conditions.
This is why “just start the foundations” can be poor advice.

Before using commencement works to preserve a permission, review the full decision notice and confirm whether anything needs to be approved first.

How Should You Prove That Planning Permission Was Commenced?

Good evidence is extremely valuable if the development is stopped after the initial commencement works and restarted years later.

Dated photographs, contractor invoices, Building Control records, site records and drawings identifying exactly where the works were undertaken can help establish what happened and when.

If there is uncertainty over whether a permission was lawfully implemented, it may also be possible to apply for a Lawful Development Certificate confirming the planning status of existing operations.

GOV.UK explains that an existing operation can be the subject of a lawful development certificate where the appropriate legal test is satisfied. Read the official Lawful Development Certificate guidance.

This can be particularly useful where an owner has carried out commencement works but does not intend to continue construction immediately.

Can You Extend Planning Permission With Section 73?

No – this is an important correction to older guidance. A Section 73 application can be used to seek permission to develop without complying with certain conditions attached to an existing permission.

However, Section 73 cannot be used to extend the deadline by which development must commence. GOV.UK’s current guidance states expressly that planning permission cannot be granted under Section 73 to extend the time limit for beginning development or the deadline for submitting reserved matters. The implementation condition must remain unchanged from the original permission. See the official Section 73 guidance.

This is one of the most important corrections to the previous 2025 version of this article. If your planning permission is about to expire and development cannot lawfully commence in time, do not assume a Section 73 application will reset the clock for another three years.

It will not.

AC Design Solution’s guide to making changes to an existing planning permission explains the distinction between Section 73 and non-material amendment routes in more detail.

What Should You Do if Planning Permission Is About to Expire?

If the deadline is approaching, first review whether the project can be lawfully commenced under the existing permission. That means checking the approved plans, commencement condition and any pre-commencement requirements. If lawful commencement is feasible, the commencement work should be clearly documented.

If commencement is not possible, the normal solution is likely to be a new planning application. A new application may use a similar design, but approval is not automatic simply because the scheme was approved before.

Planning applications are determined against the development plan and other material considerations applicable at the time of the new decision. Current policy, site circumstances and legislation therefore need to be reviewed before resubmitting.

What Happens if Planning Permission Has Already Expired?

If no lawful commencement occurred before the implementation deadline, the permission will normally no longer authorise you to begin the development.

You will usually need to submit a fresh planning application if the work still requires planning permission. Before resubmitting, review whether anything has changed since the original approval.

That can include local plan policies, conservation guidance, Article 4 Directions, design standards, planning constraints or changes to the proposed development itself. If the work could now qualify under permitted development rights, that may provide another route—but this needs to be assessed against the current legislation and the specific property.

AC Design Solution’s Permitted Development Checker can help with an initial assessment.

Does Permitted Development Permission Expire After Three Years?

Not in the same way as an ordinary full planning permission. The previous article described permitted development as “usually valid for three years”. That is too broad.

Permitted development rights arise from the General Permitted Development Order rather than from an ordinary grant of full planning permission. Different classes have different conditions, limitations and, in some cases, prior-approval procedures with their own deadlines.

You therefore cannot apply the normal Section 91 three-year planning-permission rule automatically to every permitted development project. The current government householder permitted development guidance should be checked alongside any local Article 4 Direction and the specific class being relied upon.

How Long Does Outline Planning Permission Last?

Outline planning permission operates differently from the typical householder permission. Under Section 92, applications for approval of reserved matters normally have to be made within three years of the outline permission.

Development then normally needs to begin within two years from the final approval of the reserved matters, subject again to the actual conditions imposed on the permission.

GOV.UK confirms that applications for reserved matters are normally required within three years. See the official reserved-matters guidance.

For an ordinary London homeowner planning a rear extension or loft conversion, outline permission is much less common than a detailed householder application, but the distinction matters on larger development sites.

How Much Does a New Planning Application Cost in 2026?

The old article quoted a householder planning fee of £206. That figure is no longer current. From 1 April 2026, the statutory fee in England for the enlargement, improvement or other alteration of one existing dwellinghouse is £548.

The same 2026 fee schedule lists:

These are statutory application fees and do not necessarily represent the complete professional or submission cost of preparing an application.

The government now indexes planning fees annually. See the official 2026 planning fee schedule.

How Long Does a New Planning Application Take in 2026?

For ordinary householder applications, the statutory determination period remains eight weeks after a valid application is received. Major development normally has a 13-week statutory period.

A longer period can be agreed between the applicant and the local planning authority, so the statutory period should not be presented as a guaranteed decision date.

GOV.UK’s planning guidance, updated in April 2026, confirms the 8-week period for non-major development and 13 weeks for major development. Read the current determination guidance.

Current government statistics also show that actual determination periods can extend beyond the statutory period where an extension of time is agreed.

Real 2026 Portfolio Example: 51 Thornbury Road, Isleworth

Current AC Design Solution project work also illustrates why planning dates and conditions should be treated carefully.

At 51 Thornbury Road, Isleworth, AC Design Solution prepared the planning strategy and architectural information for a sensitive backland residential development within the Spring Grove Conservation Area.

The London Borough of Hounslow’s Planning Committee resolved on 5 February 2026 to approve application P/2025/0901, subject to conditions. Hounslow’s official committee record confirms the decision and application reference.

This example demonstrates an important point about calculating how long planning permission lasts. A committee meeting date, application submission date and final permission date are not necessarily interchangeable.

For any project—including a current AC Design Solution project—the implementation deadline should be taken from the final planning permission and its commencement condition.

That is the document the project team needs to diarise. It is also a useful E-E-A-T example because it connects the guidance in this article with a genuine 2026 London planning application rather than a hypothetical homeowner scenario.

What if Planning Policies Have Changed Since Your Original Approval?

A fresh application is assessed in the current planning context. That does not automatically mean an expired proposal will be refused, but previous approval does not freeze policy indefinitely.

The planning authority will need to consider the development plan and other material considerations applicable when it determines the new application.

This is one reason to review an expired permission rather than simply uploading the old drawing package again. For householder projects, however, avoid assuming every planning-policy change discussed in broader development guidance applies to you. A good example is biodiversity net gain.

Does Biodiversity Net Gain Apply to a Householder Reapplication in 2026?

Ordinary householder development remains exempt from mandatory biodiversity net gain. This includes qualifying householder applications such as home extensions, conservatories and loft conversions.

That means the previous article’s broad statement that development must deliver at least 10% BNG was misleading when presented to typical homeowners.

Current DEFRA guidance explicitly lists householder applications as exempt. In addition, from 6 August 2026, certain developments on sites of 0.2 hectares or below are also exempt subject to the relevant conditions. Read the current BNG exemptions. BNG may still be relevant to larger residential or other development, so the application type needs to be identified correctly.

What Happened to the Four-Year Rule?

This is another major 2026 correction. The old “four-year rule” is no longer the general enforcement period for newer unauthorised operational development in England. The Levelling-up and Regeneration Act changes took effect on 25 April 2024.

For operational development substantially completed on or after 25 April 2024, the normal enforcement period is now 10 years. For qualifying operational development substantially completed before 25 April 2024, the previous four-year period can continue to apply under transitional arrangements.

GOV.UK’s current enforcement guidance sets out this distinction clearly. Read the enforcement and post-permission guidance. This issue should not be confused with how long a valid planning permission lasts.

The three-year commencement condition concerns implementing a permission you already have. The enforcement time limits concern development carried out without the required permission or in breach of planning control. If unauthorised work is already involved, see AC Design Solution’s current retrospective planning permission guide.

Can a Lawful Development Certificate Prove That Permission Was Started?

Potentially. Where physical works were carried out before the expiry date and there is later disagreement or uncertainty about whether they lawfully commenced the permission, a Lawful Development Certificate can provide a formal planning determination if the legal and evidential test is met. The application needs evidence.

Photographs alone may help, but stronger evidence can include dated contractor records, invoices, Building Control documentation, drawings and other contemporary records showing exactly what work was undertaken.

GOV.UK emphasises that a lawful development certificate is a legal confirmation of planning lawfulness rather than a new grant of planning permission.

Can I Change My Design After Planning Permission Has Been Granted?

Potentially, but the appropriate route depends on the change. A genuinely non-material change may be suitable for an application under Section 96A.

A change to conditions may potentially be addressed through Section 73, provided the statutory limitations of that route are satisfied. A more substantial change may require a fresh planning application.

Crucially, even where Section 73 is appropriate for a design or condition change, it cannot be used simply to move the original commencement deadline. AC Design Solution’s planning permission amendments guide provides more detail on the available routes.

Can I Build Smaller Than My Planning Permission?

Do not assume that building a smaller version of the approved project is automatically compliant. In some circumstances, a reduced or partially implemented scheme may be acceptable. In others, changing dimensions, form or the relationship between elements could amount to development that is materially different from the approved plans. The correct approach depends on the wording of the permission and the nature of the change.

If the scheme is changing, establish whether it needs a non-material amendment, Section 73 application or new permission before construction diverges from the approved drawings.

Planning Permission and Building Regulations Are Separate

Lawfully commencing a planning permission does not mean that all other approvals have been dealt with. Planning permission deals with the acceptability of the development in planning terms.

Building Regulations address technical matters such as structure, fire safety, ventilation, energy efficiency and construction.

For an extension, AC Design Solution may first prepare house extension drawings for the planning stage and then develop the approved design into Building Regulation drawings before construction.

The distinction matters particularly if you intend to carry out foundation or other commencement work purely to preserve a planning permission. Do not assume that planning commencement removes the need to coordinate Building Control and the construction design.

How to Avoid Letting Planning Permission Expire

The best approach is to review the permission well before the deadline rather than a few days before it expires. Check the permission date, commencement condition, approved drawings and all pre-commencement conditions. Then establish what work could genuinely and lawfully implement the approved development.

If work is carried out, keep clear contemporaneous evidence. If the project cannot commence in time, assess a fresh planning application early enough that you are not forced into rushed commencement works. And most importantly, do not rely on the outdated idea that a Section 73 application automatically gives the project another three years.