Section 73B and the limits on amending a permission

There are three ways to change a planning permission you already hold, and section 73B of the Town and Country Planning Act 1990 was designed to fill the gap between two of them. Section 96A deals with non-material amendments. Section 73 varies or removes conditions and cannot touch the description of development. Section 73B, inserted by section 110 of the Levelling-up and Regeneration Act 2023, allows an application to vary an existing permission provided the effect of the varied permission would not be substantially different from the original.

Verify the commencement position before you rely on it. As at October 2026 the drafting is on the statute book, and whether and how it has been brought into force in England is a matter to check on legislation.gov.uk and the relevant gov.uk guidance, because the implementation of the 2023 Act has been staged over several years.

The three routes to change an existing permission

Each route answers a different question, and choosing wrongly costs months.

Section 96A has no statutory definition of "non-material", which is deliberate and unhelpful in equal measure. In practice it carries minor fenestration changes, small dimensional adjustments, materials substitutions and corrections. It cannot be used where the amendment would alter what the permission is for.

What section 73 can and cannot do

Section 73 is an application for permission to develop without complying with a condition previously imposed. A successful application produces a new permission, sitting alongside the original rather than replacing it, subject to the conditions the authority imposes on the new grant.

Two limits define its reach. Section 73(5) prevents its use to extend the time limit for implementation, which closed the renewal route. And the Court of Appeal held in Finney v Welsh Ministers that a section 73 permission cannot be granted where the effect would be to vary the description of development, so a condition cannot be used as a back door to change the scheme described on the decision notice.

That second limit is what created the problem. A scheme approved as "erection of 48 dwellings" cannot become 46 dwellings through section 73 if the description names the number, even where everyone agrees the change is modest. Practitioners responded by asking authorities to grant permissions with short descriptions, which works until the authority declines.

The practical consequences of section 73 are also often overlooked. A new permission reopens no policy assessment, because the authority considers only the condition in question and its implications. But it is a new permission, so the biodiversity gain condition regime and the Community Infrastructure Levy position both need checking, and the levy consequences of a new grant are set out in commencement notices and the CIL amendment regulations.

What section 73B was designed to address

Section 73B allows an application for planning permission for development already permitted, where the development is to be carried out otherwise than wholly in accordance with the existing permission. The authority may grant it only if satisfied that its effect will not be substantially different from the effect of the existing permission.

Two features matter. The authority's consideration is focused on the difference between the existing permission and the proposed variation, rather than on a full reassessment of the scheme against current policy. And the description of development is not off limits, which is precisely the gap Finney left open.

What "substantially different" means in practice will be worked out through decisions and, in time, through appeals and the courts. Expect authorities to take different views in the early period, and expect the threshold to be read more narrowly than developers would like. A variation that changes unit numbers modestly, adjusts a building footprint, or revises a phasing plan is the kind of case the section was written for. A variation that introduces a new building, a new use or a materially larger quantum is not.

The effect of the Hillside decision on incompatible schemes

The Supreme Court's decision in Hillside Parks Ltd v Snowdonia National Park Authority restated a principle that had been understood since Pilkington: where a later permission is implemented in a way that makes it physically impossible to carry out an earlier permission in full, further development under that earlier permission becomes unlawful.

The Court was careful about what it did not decide. It did not hold that a "drop in" permission for part of a site automatically invalidates the wider permission. The question in each case is whether the original permission can still be carried out, and a departure that is not material in the context of the whole scheme does not have that effect.

What the decision did do was make everyone look at their multi-phase permissions again. A large residential permission built out over fifteen years with a series of amendments is exactly the situation where the analysis bites, because the cumulative effect of amendments may have made the original scheme impossible without anyone noticing. The Court's own observation was that where a developer wants to depart materially from an existing scheme, the orthodox course is to apply for a fresh permission covering the whole of the site as modified.

Section 73B does not solve the Hillside problem. It narrows the circumstances in which a developer has to go back for a full permission, which reduces how often the problem arises, and that is a different thing.

Choosing between section 96A, section 73 and a fresh application

Work through it in this order.

1. Is the change immaterial in itself and does it leave the description untouched? Section 96A, with a plan showing the change marked up.
2. Is the change delivered entirely by varying or removing a condition, with the description unaffected? Section 73.
3. Does the change affect the description, or exceed what a condition can carry, while leaving the overall effect broadly as permitted? Section 73B, subject to its commencement.
4. Is the change material in the context of the whole scheme, or does it make the existing permission impossible to complete? A fresh application for the whole site as modified.

The fourth option is the one developers resist and sometimes the only safe one. A fresh application reopens policy, which in a plan-making transition period is a real risk, and the position on emerging plans is discussed in plan-making reform and what happens to emerging plans. Weigh that against the risk of building out something unlawful.

Drafting applications so later amendment is possible

The easiest amendment is the one you designed for at the outset.

Keep the description of development short and functional. "Erection of up to 48 dwellings with associated access, parking and landscaping" leaves far more room than a description reciting house types and floor areas. Resist an authority's attempt to import detail into the description, and say in the covering letter that the detail belongs in the conditions and the approved plans.

On a phased scheme, define the phases in a condition with a phasing plan rather than in the description, and include a mechanism allowing phase boundaries to be amended with written approval. Consider whether each phase can stand as a self-contained permission, because severability is the practical answer to the Hillside analysis.

Keep a live schedule of every amendment made to a permission, with the route used and the date. On a long scheme that schedule is what tells you, five years in, whether the original permission can still be completed. The Planning Statement submitted with each amendment should record the amendment history rather than starting from scratch, because the officer assessing the fourth variation needs the thread.

Commencement and transitional points to verify

Three things to check at the time of writing rather than assuming.

Whether section 73B is in force in England and for what classes of permission. Whether the fee for a section 73B application has been set in the fees regulations, since no fee means no valid application. And whether the authority's own validation list has been updated to include section 73B, because validation teams work from lists rather than from statute.

Follow reform progress through the planning law timeline, and check the primary source on legislation.gov.uk before advising a client on any of this.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.