Implementation: what counts as a lawful start on site

A planning permission is implemented when a material operation is carried out lawfully on the site, and both words in that phrase do work. Section 56 of the Town and Country Planning Act 1990 lists what counts as a material operation. Case law adds that an operation carried out in breach of a condition does not implement anything at all. So a permission can be kept alive by digging a single foundation trench, and it can also be lost by digging that trench a week before the contamination condition was discharged.

The time limits on a permission

The default for a full permission is three years from the date of grant, under section 91 of the 1990 Act, though the authority can impose a different period and occasionally does on larger or more sensitive schemes. Read the condition on your decision notice rather than assuming three years.

Outline permissions work differently under section 92. Reserved matters must be applied for within three years of the outline grant, and the development must begin within two years of the final approval of the last reserved matter. Two clocks, two deadlines, and the second one is often missed by people watching the first.

There is no renewal application. The route that once allowed an extension of time was withdrawn, and section 73 cannot be used to extend a commencement period. When a permission expires, it is gone, and a fresh application is assessed against whatever policy applies at that later date.

What amounts to a material operation

Section 56(4) sets out the list. In practice these are the ones that matter on a small site:

• Any work of construction in the course of erecting a building.
• Demolition of a building.
• Digging a trench that is to contain the foundations, or part of the foundations, of a building.
• Laying an underground main or pipe to a foundation trench.
• Any operation in the course of laying out or constructing a road or part of a road.
• A material change of use, where the permission is for a change of use.

The list is generous by design. A foundation trench in the right position, dug to the right depth for the approved building, is enough. Marking out with pegs is not. Clearing vegetation is not. Erecting a site hoarding is not, because none of those are operations of the kind listed.

Position matters as much as the operation. A trench dug where the approved drawings show no foundation is not a trench for the foundations of that building. Set the works out from the approved plans and photograph the setting out.

Conditions that must be discharged first

This is where most failed implementations happen. Where a permission carries a condition requiring something to be approved before development begins, and work starts before that approval, the work is a breach of condition. Following Whitley & Sons v Secretary of State for Wales, operations carried out in breach of such a condition do not amount to a lawful start, so the permission is not implemented and the clock keeps running.

The courts have since refined the principle, and not every condition breach has that effect. Conditions going to the heart of the permission, where the whole scheme depends on approval of a fundamental matter, are treated most strictly. A condition requiring a landscaping scheme is less likely to defeat implementation than one requiring a remediation strategy for contaminated ground.

Do not rely on that distinction. The safe sequence is to discharge every pre-commencement condition, receive the written approvals, and then start. Where the authority is slow, apply early and chase in writing, because "we applied in good time" is not a defence.

Under the Environment Act 2021 regime, the biodiversity gain plan must be approved by the authority before development begins on most permissions. That is a statutory requirement rather than an ordinary condition, and a Biodiversity Net Gain Assessment prepared by a competent person sits behind it. Programme the ecology work months ahead, because survey seasons do not move for construction programmes.

Why a token start can still fail

A trench dug in the last fortnight before expiry, purely to keep a permission alive, is lawful if the operation is a material operation and no condition is breached. Inspectors and courts have accepted such starts. What defeats them is usually one of four things:

1. The works were not carried out in accordance with the approved plans.
2. A pre-commencement condition remained undischarged.
3. Another consent required for the works, such as listed building consent, had not been obtained.
4. The evidence that the works happened before expiry does not exist.

There is also a quieter risk. Once a permission is implemented, the levy and obligation position crystallises, and the developer becomes liable for community infrastructure levy on a chargeable development that may not proceed for years. Implementing to preserve optionality is not free.

Evidence to record at the moment of implementation

Assemble the file on the day, not two years later when a buyer's solicitor asks.

Where the permission is valuable and the start was late, consider applying for a certificate of lawfulness of existing development under section 191 to confirm the permission was implemented. It costs a fee and some time, and it converts an argument into a document.

Levy notices and the self-build exemption

For anyone building their own home, the community infrastructure levy sequence is unforgiving. The exemption for self-build housing has to be claimed and granted before development begins, and a commencement notice must be submitted to the collecting authority before any work starts.

Start first and the exemption can be lost outright, with the full levy becoming payable and surcharges applied. This is the single most expensive administrative error available to a self-builder, and it happens because the planning permission feels like the finish line.

Serve the commencement notice, get the acknowledgement, keep it with the file, and only then let the digger onto the site.

Permissions that cannot lawfully be implemented

Two situations arise more often than you would expect.

Where two permissions exist on the same land and it is physically impossible to build both, implementing one can make the other incapable of implementation. That matters when a site has an old permission held in reserve.

Where the works also require another consent that has not been obtained, starting is unlawful under that other regime even if the planning position is sound. Listed building consent is the common one. So is a licence for protected species, which cannot be granted retrospectively once a roost or a habitat has been destroyed.

If a permission is close to expiry, work backwards from the last day: allow eight weeks for condition discharge, time for any levy notices, and a week of contingency for weather. That usually means starting the paperwork four months out. Set out the position clearly in the Planning Statement at application stage and negotiate later triggers then, rather than fighting the sequence at the end. The full list of supporting documents shows what a scheme may need before anything can begin.

This is general guidance, not legal advice. Implementation questions turn on the exact wording of your conditions, so check the position with your local planning authority or a qualified professional before relying on it.

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