Open book viability and what becomes public

Open book viability transparency is the default in England, and it has been since the 2018 revision of the planning practice guidance. The guidance expects viability assessments to be prepared on an open book basis and to be made publicly available, with commercially sensitive detail aggregated rather than withheld wholesale. So the working assumption when you instruct an appraisal should be that your land cost, your build cost allowances and your profit assumption will be read by the parish council, by a residents' group and by anyone who follows the planning register.

What national guidance actually expects

The viability chapter of the planning practice guidance sets out standardised inputs and says assessments should reflect that approach. On publication, the position is that assessments should be made publicly available, and where a specific element is deemed commercially sensitive the information should be aggregated in published form.

Aggregation is the word to hold onto. It is not an exemption. An assessment that redacts the land value line entirely has not aggregated anything, and an officer who accepts that has accepted something the guidance does not provide for.

Two things follow from the plan-led design of the system. Viability is meant to be tested at plan-making stage, so that policy requirements are already known to be deliverable across the plan area. Where an applicant then argues site-specific viability at application stage, the burden sits with the applicant to show why the plan's assumptions do not hold. Publication is the mechanism that lets anyone check whether the argument is sound.

What gets published and what tends to stay back

In practice the published bundle on a contested major application usually includes the full appraisal with the inputs visible, the applicant's covering statement, the independent reviewer's report commissioned by the council, and the officer report that weighs the two. The section 106 agreement is a public document once completed, and any review mechanism inside it is public with it.

What councils more often agree to aggregate is narrow:

• unit-level sales values, published as an average or a range by unit type rather than plot by plot
• the terms of a specific funding facility, where disclosure would reveal a lender's commercial terms
• a contract sum from a live tender process that has not yet concluded
• personal information about individuals, which is redacted under data protection rules rather than on commercial grounds

Land value is the line applicants most want to hide and the line councils are least willing to lose, because benchmark land value is the input that decides the answer. The practice set out in independent review of a viability appraisal depends on the reviewer and the public being able to see it.

Arguing commercial sensitivity

The argument succeeds when it is specific and time limited. It fails when it is a blanket claim.

What tends to work is a request to aggregate a particular input, with an explanation of the identifiable harm, a proposed form of aggregation that still allows the figure to be tested, and an end date after which the full figure can be released. A council can defend that. What does not work is a request to withhold the appraisal pending determination, because determination is precisely when the public interest in seeing it is highest.

Be realistic about the odds. Most authorities now publish as a matter of course, several have adopted local validation requirements that make publication a condition of accepting an appraisal, and officers are reluctant to carry the information rights risk of withholding.

Freedom of information, and why the environmental route matters more

If a council does withhold an appraisal, the request route is not the Freedom of Information Act 2000. Planning information is environmental information, so the Environmental Information Regulations 2004 apply instead, and they are less favourable to the holder.

Three features of the regulations matter here. There is no absolute exemption for commercial confidentiality, only an exception at regulation 12(5)(e) for confidentiality of commercial or industrial information where that confidentiality is provided by law to protect a legitimate economic interest. Every exception is subject to a public interest test. And the regulations include an express presumption in favour of disclosure, so a tie goes to the requester.

The practical effect is that an authority refusing a request has to show the confidentiality is protected by law, that there is a legitimate economic interest, that disclosure would harm it, and that the harm outweighs the public interest in release. Each step is a place the refusal can fail, and decisions of the Information Commissioner and the First-tier Tribunal in this area have consistently given weight to the public interest in understanding how an affordable housing requirement was reduced.

Note: a refusal is appealable, which means the information may still come out, just later and with an adverse decision attached to it.

Preparing an appraisal you are content to publish

The discipline is simple and most teams resist it. Write the appraisal as though it will be read aloud at committee.

That means the inputs are evidenced rather than asserted. Sales values supported by completed comparable transactions with addresses, dates and areas. Build costs tied to a published cost index with the base date stated, and abnormals itemised line by line with the investigation report that evidences them. A benchmark land value derived by a stated method, with the comparable transactions or the existing use value calculation shown. A profit assumption with a reason for the chosen figure rather than a convention.

It also means the sensitivity analysis is in the document. If your conclusion flips when sales values move 5 per cent, say so, because an independent reviewer will find it and the discovery reads worse than the disclosure. The format conventions in viability appraisal outputs are worth following for exactly this reason.

One more habit worth adopting. Keep a separate internal appraisal for your own board, with your own assumptions, and keep the planning appraisal clean. Mixing the two produces a document with your target returns in it, which is the single most damaging thing to publish.

Redaction practice that holds up

Where aggregation is agreed, do it properly.

1. Produce a published version and a confidential version, with a schedule listing every difference between them.
2. Aggregate, do not black out. Replace plot-level values with averages or ranges by unit type.
3. Keep every figure that feeds the residual calculation visible, so a reader can reproduce the answer.
4. State the reason for each aggregation in a short note, and the date on which it expires.
5. Give the unredacted version to the independent reviewer and say in the published version that you have done so.

A published appraisal that cannot be reproduced from its own inputs is worse than useless. It invites the inference that the missing numbers are the embarrassing ones, and in a committee room that inference is usually made out loud.

What disclosure does afterwards

The reputational consequences land on your next application rather than this one. Residents' groups keep appraisals, compare them across schemes, and notice when the same developer's profit assumption moves between sites. Councillors remember a scheme where the affordable housing fell from policy compliant to nothing and the homes then sold above the appraised values.

There is a positive version of this. A developer whose published appraisals are consistent, whose abnormals turn out to be real, and whose review mechanisms have actually paid out acquires credibility that is worth real money in the next negotiation. Credibility is the only asset in viability work that compounds.

Illustrative example. A 60 unit urban scheme offering 15 per cent affordable against a 35 per cent policy, on the basis of a contaminated land abnormal and a land price agreed 2 years earlier. The land price is the vulnerability. Publishing it invites the obvious question about whether an overpayment is being passed to the council as a reduced affordable contribution, and the answer has to be a benchmark land value calculation that stands on its own, independent of what was paid.

A Viability Assessment and the Affordable Housing Statement that sits beside it should tell the same story. PlanScope drafts both from your project answers and inserts a flag wherever a site-specific figure is missing, so the appraisal inputs still come from your valuer and your cost consultant. Reports should be reviewed before submission, and viability work on a contested scheme should be prepared or signed off by a suitably qualified valuer. This is general guidance, not legal advice; check the position with your local planning authority 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.