The Finney principle and the limits of section 73

The Finney principle is simple to state and awkward to live with: section 73 of the Town and Country Planning Act 1990 cannot be used to vary a condition if the variation would conflict with the operative description of the development. The Court of Appeal decided this in Finney v Welsh Ministers [2019] EWCA Civ 1868, and it means that any number, height, unit count or drawing reference that found its way into the description of development becomes effectively unalterable without a fresh application.

For anyone drafting application forms, the lesson lands before the permission is even granted. The description you write at submission sets the limits of what you can change for the life of the permission.

What the Court of Appeal decided

The case concerned permission for two wind turbines. The description of development referred to turbines of a stated tip height, and a condition repeated that height. The developer applied under section 73 to vary the condition so that taller turbines could be built, leaving the description untouched.

The Court of Appeal held that the application could not be granted. Section 73(2) allows the authority to grant permission unconditionally or subject to different conditions, and that is the full extent of the power. It does not allow the description of the development to be altered, and it does not allow a condition to be imposed that contradicts the description. A permission for turbines of one height with a condition permitting a greater height would be internally incoherent.

The decision overturned the approach taken at first instance in an earlier High Court case that had allowed exactly that manoeuvre, so a number of permissions granted between the two decisions sit on shaky ground. Practitioners who inherited one of those should look at it carefully.

Conditions that conflict with the description

The test is conflict, not inconvenience. A condition that simply adds detail to a described development can be varied freely. A condition that restates a parameter already fixed in the description cannot be loosened, because loosening it puts the two in opposition.

Worked through on common descriptions:

Reducing a described figure raises a subtler question. A description referring to 24 dwellings is arguably not contradicted by building 22, and authorities often take that view, although the safer course where a reduction matters is to deal with it openly rather than to rely on an argument about whether the shortfall is immaterial. That is the same kind of threshold assessment that runs through de minimis judgements in planning, and it is decided on the facts.

Why the description matters at application stage

Case officers rarely rewrite a description, and applicants rarely think about it. Between those two habits, a great deal of avoidable rigidity enters the system.

The description is taken from the application form. If the agent writes "Erection of 14 no. two and three bedroom dwellings with associated parking and landscaping, in accordance with drawings listed in the schedule", every one of those elements is locked. Change the mix from two and three bedroom to include a four bedroom unit and the permission no longer authorises what is being built, and section 73 is not available to fix it.

There is a counter-pressure. Authorities want descriptions that are precise enough for the public to understand what is proposed from the site notice, and precise enough that the permission is enforceable. A description reading "development" would be unlawfully vague. Community infrastructure levy liability, affordable housing obligations and section 106 triggers are also often tied to unit numbers, and an authority may insist on the count appearing somewhere.

The resolution is to put precision in conditions rather than in the description. A condition requiring development in accordance with an approved drawing schedule gives the authority full control and leaves section 73 open, which is exactly where a well-advised applicant wants to be.

Drafting a description that preserves flexibility

Four habits make a measurable difference.

• Describe the use and the operation, not the specification. "Erection of a detached dwelling and garage" rather than "Erection of a four bedroom detached dwelling of 186 square metres with a double garage".
• Keep drawing numbers out of the description. Put them in a plans condition. This single change is the most useful of the four, because drawing substitution is the most frequent reason for a later variation.
• Avoid dimensions, heights, capacities and covers in the description unless the authority insists. Where it does insist, ask for the figure to be framed as a maximum, which gives room below it.
• Where unit numbers must appear, consider "up to" wording. Authorities are not obliged to accept it, and some will not, but it is worth asking.

None of this is about concealing the proposal. The drawings, the schedules and the supporting documents still describe the scheme in full, and the Planning Statement is where the proposal is explained properly. It is about not fossilising detail in the one sentence that cannot later be amended.

Where section 73 is closed off

When a variation is blocked by the description, three routes remain.

A fresh application under section 70 for the whole development is the orthodox answer. It carries a full fee, full consultation, a fresh assessment against the policies current at the time, and a new section 106 agreement or a deed of variation. On a scheme with a viability history or a changed policy background, that reassessment is the real risk rather than the fee.

A non-material amendment under section 96A can add, remove or alter conditions, but planning practice guidance is clear that it cannot be used to change the description of development. So section 96A does not rescue a description problem either, and the threshold for non-materiality is low.

The third route is section 73B of the Town and Country Planning Act 1990, inserted by the Levelling-up and Regeneration Act 2023, which is intended to allow variations where the effect of the development as varied is not substantially different from that of the existing permission, including changes to the description. As at October 2026, check whether the section is in force in England and what the accompanying procedure requires, because the practical value of the route depends entirely on how it is brought into force and on how authorities apply the substantial difference test.

Two further limits on section 73 are worth remembering. It cannot be used to extend the time limit for implementation, and a grant under section 73 creates a new, freestanding permission that sits alongside the original rather than replacing it, so the original remains capable of implementation unless and until it lapses.

The effect on minor material amendments

The minor material amendment is an administrative label rather than a statutory one. It describes a section 73 application for a change the authority considers minor, and it carries all of the section 73 limits.

So the Finney principle applies to every minor material amendment. An authority that accepts a minor material amendment application to increase a described unit count, or to substitute a drawing named in the description, is acting outside the power, and the resulting permission is vulnerable. Some authorities now check the description as a validation step for exactly this reason, which is one of the quieter causes of applications being returned as invalid or redirected to a different route.

Where the amendment touches outline permission, remember that the parameters approved at outline stage and the matters left for later approval work differently again, and what can and cannot be reserved determines the route rather than section 73.

Checking a proposed variation

A five-minute check before you advise a client.

1. Pull the decision notice and read the description of development word for word, including any figures, drawing numbers or qualifiers.
2. List every parameter the description fixes.
3. Compare the proposed change against that list. Any overlap means section 73 is closed.
4. If there is no overlap, identify the condition to be varied and confirm it is not the time limit for starting work.
5. Check whether the change triggers anything collateral: community infrastructure levy recalculation, a section 106 variation, fresh consultation, or a new screening opinion where the original was Environmental Impact Assessment development.
6. Where section 73 is closed, price the alternatives properly, including the policy risk of a fresh assessment, before recommending one.

The honest uncertainty here is the substantial difference test under the newer provision. Until there is a body of decisions applying it, nobody can say with confidence where the line sits, and advice to clients should say so rather than imply a settled position.

This is general guidance rather than legal advice, so check the position with your local planning authority or a qualified professional before relying on it.

If you are preparing the supporting case for a variation or a fresh application, browse the 66 report types to see which documents the revised scheme is likely to need.

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