Varying a permission for development already begun

A section 73B application is the route Parliament created for a change that is too large for a non-material amendment and too small to justify starting again, including a change to development that has already been built. It was inserted into the Town and Country Planning Act 1990 by section 110 of the Levelling-up and Regeneration Act 2023. The gate is a single test. The local planning authority has to be satisfied that the effect of the permission as varied would not be substantially different from the effect of the existing permission.

Before you programme an application around it, check whether the section has been brought into force and whether the fee and procedure regulations that go with it have been made. As at October 2026 the safest assumption on any live scheme is that you verify the position on legislation.gov.uk and with the case officer rather than relying on a secondary account of it.

What the section provides for

Three features set it apart from the older routes. It can alter the description of development. It can alter, remove or add conditions and other operative parts of the permission. And it is available where the works have already been carried out, which the older routes handle badly.

That combination matters more on site than it reads on the page. A housebuilder who has set a terrace 600mm further back than the approved layout, or lifted a ridge by 300mm to deal with ground conditions, has until now had three unattractive choices: a non-material amendment under section 96A that the officer may refuse because the change is not non-material, a section 73 application that cannot touch the description of development, or a retrospective application under section 73A that reopens the permission in full.

The new route is aimed squarely at that gap.

The test the authority applies

The authority may grant the varied permission only if it is satisfied that its effect will not be substantially different from the effect of the existing permission. Two points follow for anyone drafting the submission.

First, the comparison is between permissions, not between the scheme and the development plan as a whole. The existing permission is the baseline and the question is what changes about its effects. Height, massing, overlooking, parking, drainage discharge, trip generation, hours of use: each needs a before and after position.

Second, "substantially different" is a judgement, so the application has to do the work of showing why the difference is modest. Reciting that the change is small will not carry it. A short comparison schedule, drawing by drawing, with the quantified difference against each approved drawing number, is worth more than several pages of narrative. Where the difference is nil, say so and show the drawing reference.

Keep the policy argument proportionate. If the varied scheme engages a policy the original did not, for example because floorspace crosses a parking standard threshold, that is the point at which the effect starts to look substantially different and the route starts to look wrong.

How it differs from section 73 and section 96A

The three routes are not interchangeable, and choosing the wrong one costs weeks.

The constraint on section 73 comes from the Court of Appeal decision in Finney v Welsh Ministers in 2019, which confirmed that a condition cannot be varied in a way that contradicts the operative description of what was permitted. That is why a scheme described as "erection of 14 dwellings" cannot become 15 by varying a plans condition. Section 73 also cannot be used to extend the life of a permission, and section 73(5) says so. Read the equivalent provisions in section 73B before you assume the position is different there.

Section 96A has one practical advantage worth keeping in mind. It is quick, usually determined inside 28 days, and it carries no publicity requirement. It also carries no right of appeal if the authority refuses, which is the trade-off.

Development already carried out

Where the works are built, the sequence of events changes the risk. A section 73A application invites the authority to assess the development as it stands against current policy, with the original permission reduced to background. On a scheme consented under an earlier version of the development plan, or before mandatory biodiversity net gain applied, that reopening is the real exposure rather than the amendment itself.

A variation route that keeps the original permission alive and asks only about the difference in effect protects that position. It does not cure an enforcement risk on its own. Until the varied permission is granted, the building sits outside what was authorised, and the authority's enforcement powers are unaffected by the existence of a pending application.

Two practical steps reduce the exposure. Tell the case officer before submission, in writing, what has changed and why. And keep the as-built survey evidence, because the comparison schedule stands or falls on measured dimensions rather than on contractor assurances.

Where the project needs a supporting narrative setting out the policy position on the change, a focused Planning Statement addressed to the difference in effect is more use than a general one that restates the original case.

Whether the route is in force, and what to check

A provision on the statute book is not a provision in force. Section 110 of the 2023 Act depends on regulations bringing it into force, and the route also needs an application form, a publicity requirement and a fee before an authority can accept it. Check three things before you rely on it: the in-force position for section 110 on legislation.gov.uk, the current fee schedule, and whether the authority's own validation list refers to the route at all.

If any of those is missing, the honest answer to a client is that the application must take one of the existing routes. That is less satisfying than describing the new one, and it is what keeps a programme intact.

Choosing between the routes on a live scheme

Work through it in this order.

1. Define the change in measured terms against the approved drawing numbers, including what has already been built.
2. Ask whether the change conflicts with the description of development. If it does, section 73 is closed to you.
3. Ask whether the change is capable of being called non-material. If the officer agrees in pre-application correspondence, section 96A is the fastest route and the least costly.
4. If the change is material but the effects are close to the original, test whether the section 73B route is available and what the fee would be.
5. If none of that works, budget for a fresh application and the current policy requirements that come with it, including biodiversity net gain where it applies.

Obligations are a separate exercise. A varied permission does not automatically carry the original section 106 agreement with it, so the deed needs checking and often a supplemental agreement, which is covered in our note on varying a section 106 agreement after permission. Fees also move, and some changes attract reductions worth claiming, which we set out in the guide to planning fee exemptions and reductions.

An illustrative example: a consented scheme of nine houses where the plot 4 garage was built 1.2m wider to suit a retaining wall. The description says "erection of 9 dwellings with associated garages", so section 73 is available for the plans condition only if the wider garage does not conflict with that description. The officer's view on overlooking and on the parking layout decides whether a non-material amendment is realistic. The comparison schedule, one line per drawing, is what settles it either way.

Enter your postcode on PlanScope to see which supporting reports a variation application is likely to need before you commit to a route.

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.