Less than substantial harm: the heritage balance explained

Less than substantial harm is the lower of the two categories of harm to a designated heritage asset in national planning policy. It covers everything from a barely perceptible change in the setting of a listed building to serious erosion of significance that still stops short of destroying what matters about the asset. Once a decision-maker lands in that category, the harm has to be given great weight and then weighed against the public benefits of the proposal. Put the harm in the wrong category in a heritage statement and every argument that follows it is built on sand.

Where the categories of harm come from

The split between substantial harm or total loss on one side and less than substantial harm on the other sits in the historic environment chapter of the National Planning Policy Framework. The Framework was re-issued on 17 August 2026 and its chapters now carry policy codes rather than the paragraph numbers practitioners quoted for a decade, so take the code from the edition open in front of you rather than from an old report or a template.

The two-category structure has been stable in substance since 2012 even as the numbering moved. What changes between editions is the wording around public benefits, optimum viable use and the treatment of assets of the highest significance, which is why a heritage statement that recycles a 2019 policy quotation reads as careless to a conservation officer.

Neither category is defined in the Framework itself. The content comes from the courts and from Planning Practice Guidance, which describes harm as arising where a proposal erodes the elements that contribute to significance.

The statutory duty that sits behind them

Policy categories do not displace statute. Section 66(1) of the Planning (Listed Buildings and Conservation Areas) Act 1990 requires the decision-maker to have special regard to the desirability of preserving a listed building, its setting and any features of special architectural or historic interest it possesses. Section 72 imposes a parallel duty to pay special attention to preserving or enhancing the character or appearance of a conservation area.

The Court of Appeal in Barnwell Manor Wind Energy Ltd v East Northamptonshire District Council [2014] EWCA Civ 137 settled what that duty means in practice. The statutory duty creates a strong presumption against granting permission where harm is found, and considerable importance and weight must be given to that harm when the planning balance is struck. Crucially, the duty bites even where the harm is at the lowest end of the less than substantial range.

So a heritage statement that says the harm is "minor and therefore acceptable" has skipped a step. Minor harm still attracts the statutory presumption. The question is whether something on the other side of the scale outweighs it.

Identifying the level of harm

Substantial harm is a high bar. In Bedford Borough Council v Secretary of State for Communities and Local Government [2013] EWHC 2847 (Admin) the High Court accepted that harm is substantial where it is serious enough to drain away or vitiate the significance of the asset, or a very large part of it. Very few schemes involving alteration or development in a setting get anywhere near that.

That leaves a wide band. Less than substantial harm runs from the almost imperceptible to the severe, and the assessment has to say where in that band the proposal falls. Vague phrasing invites an officer to pick their own point on the scale, usually higher than yours.

Work through it in a fixed order:

1. State what the significance of the asset is, drawing on the list entry, the Historic Environment Record and what you can see on site, using the interests set out in Historic England's advice on assessing significance.
2. Identify which attributes of that significance the proposal touches, including the contribution setting makes.
3. Describe the change to each attribute, in terms a reader can picture: the loss of a rear wall, the interruption of a designed view, the introduction of movement into a static agricultural setting.
4. Conclude on the level of harm, and say whether it sits at the lower, middle or upper end.
5. Explain what design changes have already reduced it.

The fourth step is where most drafts go quiet. Write the sentence.

What counts as a public benefit

Public benefits are benefits that flow to the public at large, not private gains to the applicant. Planning Practice Guidance on the historic environment is explicit that they can be heritage benefits, such as securing the optimum viable use of a building at risk, or wider benefits such as housing delivery, employment, public access or environmental improvement.

Three traps recur. The first is counting the repair of the asset itself as a benefit when the repair is simply the consequence of the works being done, with no obligation to carry it out. The second is claiming economic benefit with no evidence, which invites the officer to discount it. The third is padding the list, because a page of small benefits reads as weaker than three substantiated ones.

Benefits need securing. A benefit delivered by condition or by a section 106 obligation carries weight. A benefit described in a covering letter does not. Where the benefit is the reuse of a building, the Heritage Statement should say what the alternative is if the scheme is refused, and be honest when the answer is that the building simply stays as it is.

How the balance is struck in practice

The Framework asks whether the public benefits outweigh the harm. Read with section 66 and the case law, that becomes a weighted exercise rather than a straight comparison, with considerable importance and weight loaded onto the heritage side before anything else is added.

An illustrative example helps. Take a Grade II former agricultural building in open countryside, proposed for conversion to a single dwelling with a glazed link and two rooflights on the rear slope. The harm is the loss of legibility of the threshing floor opening and the domestication of an agricultural setting, which sits at the lower end of less than substantial. The benefits are a secured repair programme for the roof structure written into a condition, removal of a modern lean-to that obscures the original elevation, and one additional dwelling in a district that cannot demonstrate a five-year supply. On those facts a decision-maker could reasonably conclude the benefits outweigh the harm. Change one variable, say the building is already in good repair, and the balance shifts.

That is the level of specificity a heritage balance needs. Generic assertions that "the benefits of bringing the building back into use clearly outweigh any limited harm" do not survive a careful officer, and they certainly do not survive an inspector.

Total loss and substantial harm compared

Where the finding is substantial harm or total loss, policy applies a much tighter test. Consent should be refused unless it can be demonstrated that the harm is necessary to achieve substantial public benefits that outweigh it, or unless a short list of conditions is met, including that no viable use can be found, that grant funding is unavailable and that the harm is outweighed by bringing the site back into use.

Policy then splits the substantial harm category in two. Assets of the highest significance, including scheduled monuments, protected wreck sites, registered battlefields, Grade I and II* listed buildings, Grade I and II* registered parks and gardens and World Heritage Sites, attract the stricter formulation: substantial harm or loss should be wholly exceptional. Every other designated asset gets the milder version of the same sentence. Those are different words doing different work, and quoting the wrong one is a familiar drafting error.

Presenting the balance in a heritage statement

Give the balance its own heading and its own conclusion. Do not bury it under "planning considerations" three quarters of the way down. An officer writing a delegated report wants a passage they can quote.

Set out the finding on significance, the finding on harm with its position in the range, the public benefits with the mechanism that secures each one, and then the conclusion. Where archaeology is affected as well as built fabric, the setting analysis in the heritage statement and the findings of an Archaeological Desk-Based Assessment need to agree with each other, because contradictions between supporting documents are noticed.

Check that the development plan policies you cite are actually adopted and up to date, since what counts as the development plan decides what section 38(6) requires the decision-maker to start from. Local heritage policies often add tests that national policy does not, particularly on shopfronts, boundary treatments and materials.

One honest uncertainty: nobody can tell you exactly where "lower end" stops and "middle" begins. Conservation officers disagree with each other about it. What you can do is show your reasoning attribute by attribute so that a reader who disagrees with your label still follows how you got there.

PlanScope drafts a Heritage Statement structured to the significance, harm and public benefit sequence and flags the site-specific facts it cannot verify. Enter your postcode on PlanScope to see which reports your site is likely to need, then send the draft for professional review.

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.