Less than substantial harm and the public benefits balance

Less than substantial harm and public benefits is the heritage balance most applications turn on, and it is the exercise decision-makers most often get wrong. The order matters. Identify the significance of the asset, then the harm, then apply the statutory duty, and only then weigh the public benefits. Running the balance before the duty produces a decision that reads well and falls over on challenge.

The label itself misleads. Less than substantial harm covers everything short of the very serious end, so it includes harm that is nearly substantial as well as harm that is barely perceptible. Treating it as a synonym for "minor" is the single most common drafting error in heritage statements.

The statutory duties come first

National policy sits on top of two statutory duties, and the duties are not optional.

Section 66(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 requires the decision-maker, in considering whether to grant permission for development which affects a listed building or its setting, to have special regard to the desirability of preserving the building, its setting and any features of special architectural or historic interest it possesses.

Section 72(1) applies the equivalent duty in a conservation area, requiring special attention to be paid to the desirability of preserving or enhancing its character or appearance. Section 16(2) applies to listed building consent itself.

The Court of Appeal in Barnwell Manor settled what "special regard" means in practice. Harm to a listed building or its setting must be given considerable importance and weight, and the decision-maker cannot approach the exercise as though the competing considerations start level. There is a strong presumption against granting permission where harm is identified.

That is a statutory obligation, not a policy preference, and it survives whatever the development plan says.

Substantial and less than substantial harm

The National Planning Policy Framework, in its August 2026 edition, splits harm to designated heritage assets into two categories with very different consequences.

Substantial harm or total loss is permitted only in narrowly defined circumstances. For assets of the highest significance, including grade I and II* listed buildings, scheduled monuments, protected wreck sites, registered battlefields, grade I and II* registered parks and gardens and World Heritage Sites, those circumstances are described as wholly exceptional. For other designated assets the wording is similar but pitched a notch lower. Either way the applicant has to show substantial public benefits that outweigh the loss, or satisfy a tightly drawn set of alternative tests about viable use and conservation by grant funding.

Less than substantial harm is weighed against the public benefits of the proposal, including where appropriate securing its optimum viable use.

The boundary between the two is not a percentage of the building. The authorities describe substantial harm as harm that drains away or vitiates a large part of the significance of the asset, so a small physical intervention at the heart of what makes a building interesting can be substantial, and the loss of a large but unremarkable rear wing may not be.

Get the categorisation wrong and the whole decision is wrong, because the policy tests are entirely different.

Why great weight is not a percentage

Great weight, considerable importance and weight, a strong presumption. The language sounds like it should translate into a number, and it does not.

What the duty requires is that the decision-maker recognises the harm as a matter that carries more force than an ordinary planning objection, and then explains why the benefits nonetheless outweigh it. A judgment that lists three harms and four benefits and concludes that four beats three has not applied the duty.

Two practical consequences follow.

First, the scale of harm has to be articulated. "Less than substantial harm at the lower end of the spectrum" is a meaningful finding. "Less than substantial harm" on its own leaves the reader unable to see how much weight was applied.

Second, the benefits have to be commensurate. Harm at the upper end of the less than substantial range needs benefits of real substance, not a landscaping contribution.

A Heritage Statement that follows Historic England's advice on assessing significance, and that grades the harm on the spectrum rather than merely naming the category, gives the officer something they can adopt. One that asserts no harm at all when the conservation officer can see harm loses credibility on everything else it says.

What counts as a public benefit

Planning practice guidance on the historic environment is clear that public benefits may be anything that delivers economic, social or environmental objectives as described in the Framework. They should be of a nature or scale to be of benefit to the public at large and should not be a private benefit.

Benefits that regularly carry weight:

1. Securing the optimum viable use of a heritage asset that is redundant or deteriorating.
2. Repair and reinstatement that removes existing harm to significance, such as taking off a poor 1970s extension.
3. New public access, interpretation or the recording of an asset before change.
4. Housing delivery, employment floorspace and other development plan objectives, where the scheme actually delivers them.
5. Environmental gains such as decarbonisation of a historic building, where they are demonstrated rather than asserted.

Benefits that carry little weight: the applicant's return, compliance with obligations the scheme would have to meet anyway, and mitigation that merely reduces the harm the proposal itself creates. Mitigation is not a benefit. It changes the level of harm.

Where the scheme involves loss of historic fabric, a programme of recording is mitigation of a sort and is usually secured by condition. A Historic Building Recording exercise to the appropriate Historic England level preserves information, and the guidance is explicit that recording does not reduce the harm.

Running the balance in practice

A defensible balance has a visible sequence.

Describe the asset and its significance, drawing on the archaeological, architectural, artistic and historic interests. Identify how the proposal affects that significance, including the contribution setting makes to it. Categorise the harm and place it on the spectrum. Apply the statutory duty and say that you have. List the public benefits with evidence for each. Then explain, in words, why the benefits do or do not outweigh the harm given the weight the duty requires.

On a scheme where setting is the issue, a Townscape and Visual Impact Assessment provides the visual evidence for the setting analysis, though it does not substitute for the significance assessment itself. The two documents answer different questions and both get read.

One further point that catches consultants out. Where a designated heritage asset provides a clear reason for refusing the development, the presumption in favour of sustainable development in the Framework does not apply in the tilted form. The heritage policies operate as a restriction, so the tilted balance argument that works on a housing land supply appeal simply is not available.

Recording it in the officer report

Members and inspectors are not required to use magic words, but the reasoning has to be capable of being followed.

An officer report that works will state the significance of the asset, the harm found, the level of that harm, an acknowledgement of the statutory duty and the considerable importance and weight it demands, the benefits relied on, and the conclusion. Where committee departs from the recommendation, the minutes need to carry the same chain of reasoning or the decision is vulnerable.

Applicants can help. Draft the heritage section of the planning statement so that an officer can lift the structure straight into the report. Officers under time pressure adopt clear reasoning and rewrite muddled reasoning, and the rewrite rarely favours you.

Errors that lead to a successful challenge

The recurring failures are worth naming.

Assessing harm without first assessing significance. Treating less than substantial harm as a low bar. Failing to apply the section 66 or 72 duty at all, or applying it only to the listed building and not to its setting. Counting mitigation as a public benefit. Relying on private financial benefit. Applying the tilted balance where policy disapplies it. And using a heritage consultant's conclusion of no harm when the council's own conservation officer disagrees, without engaging with the disagreement.

Non-designated heritage assets follow a different route. There the Framework asks for a balanced judgement having regard to the scale of any harm or loss and the significance of the asset, with no statutory duty and no presumption. Do not import the designated tests into that judgement.

Enter your postcode on PlanScope to see which heritage documents your site is likely to need before you commission a specialist.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and note that heritage assessment is normally expected from a suitably qualified author. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.