Peer review and second opinions on technical evidence

Peer review of technical evidence comes in two forms, and they behave very differently. One is a second opinion you commission yourself, to test a report before it goes anywhere. The other is a review the local planning authority commissions and you pay for, where the reviewer's client is the council and you see the output when it lands in the case file. Both are worth understanding before the first one arrives unannounced, because a scheme that has budgeted for neither can lose two months to a review it did not know was coming.

When a second opinion earns its fee

The test is simple arithmetic. If the report drives a decision worth substantially more than the review costs, review it.

Four situations meet that test regularly.

A viability assessment that determines an affordable housing contribution. A biodiversity metric where the unit deficit will be bought off site at a price per unit. A transport assessment that triggers junction mitigation. And a contamination remediation strategy where the treatment approach sets the earthworks budget.

There is a fifth, less obvious one. Where you are relying on a report you did not commission, a review usually costs less than the argument you will have if it turns out to be wrong. The questions that raises about duty of care are the same ones covered in the note on who carries the liability when work is sub-let.

Review before submission, not after. A review that changes an input is a revision. A review that changes an input after a consultee has commented is a new document, a new consultation and a new officer report.

Reviews the council commissions and you pay for

This arrangement is standard on viability and increasingly common elsewhere. The council instructs an independent consultant to audit your submission, the consultant reports to the council, and you meet the fee.

It appears most often on:

• Viability assessments, where the review follows the RICS professional standard on financial viability in planning.
• Biodiversity net gain metrics, where councils without in-house ecological capacity buy it in.
• Basement impact assessments, which several London boroughs require to be independently audited as a matter of policy.
• Transport assessments on larger schemes, where the highway authority lacks modelling capacity.
• Structural and heritage evidence where demolition is proposed.

Get the arrangement documented. The fee, the scope, the reviewer's identity, the timetable and what happens to the review output should all be agreed in writing, usually through a planning performance agreement or a specific side agreement. An open-ended commitment to pay for a review with no scope and no deadline is a position nobody should accept.

Ask two questions before you sign. What is the reviewer being asked to do, and will you see the review and have an opportunity to respond before it informs the officer report. The answer to the second should be yes, and it is worth writing down.

What a review covers and what it does not

A review tests method, inputs, assumptions and the logic connecting them to the conclusions. It works from the submitted report and the data behind it.

A fresh report re-does the work, including the survey, the modelling or the appraisal. It costs several times as much and takes several times as long.

That distinction matters when a reviewer says the assessment is inadequate. Inadequate in a review sense usually means the evidence does not support the conclusion, which can be fixed by supplying the evidence. It does not automatically mean the conclusion was wrong.

Insist that a review states which of its comments are matters of professional judgement and which are errors of method or arithmetic. Those are different categories and they deserve different responses.

How reviewers get chosen

Councils generally use a framework panel or a list of consultants they have used before. Some go to a professional body register.

Two things are worth checking. Sector experience, because a reviewer who audits city centre viability appraisals for a living may have limited feel for a rural conversion. And conflicts, because in a small market the reviewer may have acted for an objector, a competitor or a previous owner of the site.

Raising a conflict is not an attack on anyone's integrity. It is a question the reviewer's own professional body expects them to answer, and it is better asked at appointment than after the report lands. The same due diligence applies when comparing fee quotes for a specialist report in the first place.

When the review disagrees with your consultant

Resist the first instinct, which is usually to send a rebuttal letter.

A better sequence:

1. Ask your consultant to produce a table listing every review comment, with the response and the category: accepted, accepted with amendment, or disputed.
2. Narrow the disputed items to their underlying inputs. Most disagreements in viability come down to two or three numbers, and most in transport to trip rates and distribution.
3. Ask for a technical meeting between the two consultants without the planning officer present, then with them.
4. Produce a short note of agreed and disagreed points, signed by both, with the reasons for each remaining disagreement.

That note is worth more than any amount of correspondence. It lets the officer write a recommendation, it narrows what a committee has to weigh, and if the case goes further it becomes the basis of a statement of common ground.

Where a Viability Assessment is the document in dispute, remember that national guidance expects viability evidence to be publicly available, so the exchange is likely to be read by objectors as well as by the officer. Write accordingly.

Using review evidence at appeal

At appeal, a reviewer's report becomes part of the evidence and the reviewer may appear as a witness.

Two points follow. An expert witness owes a duty to give independent opinion regardless of who pays them, and an inspector will notice a witness who reads as an advocate. And a party whose behaviour has been unreasonable, including pursuing a technical objection that the evidence does not support, may face an application for costs.

Statements of common ground do a large amount of work here. An appeal where the technical evidence has been narrowed to three disputed inputs is shorter, less costly and more predictable than one where two reports sit side by side disagreeing about everything.

Budgeting and programming for it

Put a line in the budget for review, both yours and the council's. On a major application, treat an authority-commissioned review as likely rather than possible.

Put it in the programme too. A viability review can take several weeks from instruction to report, and longer if the reviewer asks for information your appraisal did not include. Build the review, the response and the technical meeting into the determination timetable, and agree an extension of time that reflects it rather than discovering the clock has run out.

Specialists who take on review work, and applicants looking for an independent reviewer, can find the route through the professional directory. To see which report types carry a professional requirement before you commission anything, browse the report types by category.

An AI-assisted draft can build the structure of a response to a review, assemble the policy framing and set out the comment table, then flag the technical inputs it does not hold. The judgements in response belong to the consultant whose name is on the original report.

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.