Section 73B: the minor variation route and what it changes

Section 73B of the Town and Country Planning Act 1990, inserted by the Levelling-up and Regeneration Act 2023, creates a route for varying a planning permission where the effect of the varied permission would not be substantially different from the permission already granted. Unlike section 73, it can alter the description of development. That single ability is what practitioners have wanted for years.

Before building a programme around it, check whether the section is in force. It requires commencement and the supporting procedural and fee provisions, and as at September 2026 the working assumption for most practices is that section 73, section 96A and a fresh application remain the available routes. Verify the current commencement position on legislation.gov.uk rather than relying on any article, including this one.

What section 73B was inserted to solve

Section 73 lets an authority grant permission for development without complying with a condition attached to an earlier permission. It has always had a boundary problem: a condition cannot be varied in a way that conflicts with the operative description of the development.

The Court of Appeal made that explicit in Finney v Welsh Ministers in 2019, where the description of development specified turbine height and the applicant sought to vary the approved drawings condition to build taller. The court held that section 73 could not be used to achieve something the description prohibited. The practical result was that a scheme whose description mentioned the number of dwellings, the floorspace or a dimension needed a fresh full application for changes that were, in planning terms, minor.

Later cases softened the position on how large a change section 73 can carry where the description does not conflict, and Armstrong in 2023 is the one usually cited. The conflict problem itself remained, and the drafting habit of putting numbers in descriptions meant it bit often.

The substantially different effect test

Section 73B asks a different question from section 73. It looks at the effect of the permission as varied compared with the effect of the existing permission, and allows the variation only where that effect would not be substantially different.

Three features follow from the wording. The comparison is with the existing permission, including its conditions, rather than with the site as it stands. It is a test about effect, so the evidence that matters is technical: daylight, transport, noise, drainage, heritage, landscape. And it is a judgement for the authority, which means it will be exercised differently between authorities until appeal decisions build up a pattern.

Do not expect a numerical threshold. There is no percentage of floorspace or number of units that makes a change substantially different, and anyone who tells you otherwise is guessing.

How it compares with section 73 and section 96A

Section 96A remains the right tool for a genuine non-material change, such as a window reposition or a drawing revision that alters nothing anyone would notice. It produces an amended permission rather than a new one, which keeps the original commencement date and avoids a fresh liability assessment.

Section 73 continues to work well where the description is drafted in general terms. If the description reads "erection of a dwelling" rather than "erection of a four bedroom dwelling with a 1.8 m boundary wall", a lot can be varied through the conditions without any conflict.

Descriptions of development and the drafting lesson

The Finney problem is a drafting problem as much as a statutory one. Descriptions that recite unit numbers, floor areas, storey heights and building dimensions import those figures into the permission as a constraint that conditions cannot contradict.

So when you submit an application, propose a description that describes the development and leaves the detail to the approved drawings. "Erection of 48 dwellings with associated access, parking and landscaping" is specific enough to define what was permitted. Adding the floorspace, the storey heights and the tenure split gives a future you four extra ways to be told no.

Watch what the validation team does with your wording. Descriptions are sometimes rewritten at registration, and the version on the decision notice is the one that counts. Check it when the notice arrives, and ask for a correction promptly if it has changed.

Fees, publicity and appeal rights

Section 73 applications attract the reduced fee for variation of conditions, are publicised in the same way as other applications, and carry a right of appeal. Section 96A has its own lower fee and no appeal right.

For section 73B, the fee, the publicity requirements, the determination period and the appeal position all sit in the procedural provisions that accompany commencement. Until those are in place, any statement about what a section 73B application will cost is speculation. Fees across the system are also indexed, so check the current fee schedule on the day you submit rather than reusing a figure from a previous project.

Two consequences that apply to any variation producing a new permission, and which get overlooked:

• the levy position is recalculated against the new permission, with abatement provisions where the earlier development has already begun, so ask the charging authority before you submit
• an existing section 106 agreement usually needs a deed of variation to attach to the new permission, and the authority's legal team will not begin drafting until the planning case is resolved

Drafting a variation application that survives scrutiny

Whichever route applies, the submission does the same job: it shows the decision taker exactly what is changing and why the effects do not shift.

1. A schedule of changes, listing the consented drawing number and revision against the proposed one for every drawing affected, with a one line description of the change.
2. A comparison table of the quantitative measures the authority cares about: unit numbers and mix, floorspace by use, parking, height in metres, site coverage, amenity space.
3. The technical evidence, updated rather than restated. If heights change, update the daylight work. If the mix changes, update the transport and refuse assumptions. Where nothing changes, say so and explain why.
4. A short statement addressing the test directly, in its statutory words, with the reasons the effect is not substantially different.
5. A note on the section 106 position and the levy position.
6. Clean drawing numbering, with a new revision letter and a revision cloud or a change note on each sheet.

A Planning Statement is the natural home for the comparison and the test. Keep it short. A variation statement that runs to 40 pages invites the officer to wonder what is being buried in it, and the officer's report has to repeat the comparison anyway.

The honest uncertainty here is how authorities will read "substantially different" in the first year or two. Some will treat it as close to the non-material threshold, others as a wide power. Until there is a body of appeal decisions, build programme contingency into any scheme that depends on a variation being accepted, and keep the option of a fresh full application open.

What to do while the position settles

Draft descriptions loosely, keep drawings numbered so that a variation can be described cleanly, and record the reasons for each design change as it happens, because the case for "no substantial difference" is easier to write when the reasoning was captured at the time.

Follow the commencement position rather than assuming it. The planning law updates timeline is a place to watch for reform news, and the statutory position itself is on legislation.gov.uk. Reform under the 2023 Act has arrived in stages, as the plan-making changes described in local plan reform under the 2023 Act show, and policy has moved underneath it with the restructured Framework covered in the 2026 NPPF.

To draft the supporting statement for a variation application, start from the postcode on PlanScope and answer the guided questions.

This is general guidance rather than 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.