When two consultants' reports contradict each other

Officers treat an internal contradiction between two of your technical reports as a credibility problem rather than a technical one. If the transport assessment counts 48 units and the energy statement counts 52, the officer does not know which document to trust, and the honest conclusion available to them is that nobody checked. Contradictory consultant reports in a planning submission are one of the most common avoidable causes of a validation query, and they cost weeks.

The underlying issue is almost never that one consultant is wrong. It is that the scheme moved and not everybody got the memo.

How contradictions get into a submission

Five mechanisms account for most of them.

The scheme changed between commissions. The ecologist surveyed in May against a layout that was revised in August, and their report describes a hedgerow that the current layout removes.

The red line moved. A site area of 0.48 hectares in the planning statement and 0.52 in the drainage calculation means somebody is working to a superseded site plan, and the difference may straddle a policy threshold.

The baseline differs. Two consultants counted the existing floorspace differently because one measured gross internal area and the other gross external, or one included a lean-to that the other treated as demolished.

The assumptions diverge. The transport consultant assumed 1.2 parking spaces per unit from the adopted standard while the layout shows 0.9, because the architect was working to a draft policy.

And the simplest one: a report was updated and a superseded version went into the submission bundle. That happens to good practices on busy weeks.

The cross-check before submission

Build a consistency matrix and fill it in from every document in the pack. It takes an hour and it catches nearly everything.

Then do the second pass, which is the one people skip: check that each technical report names the drawing revision it assessed. A report that does not say which layout it modelled cannot be reconciled with anything, and an officer who spots that will ask.

Where the pack is large, put the matrix in the covering letter as a schedule of consistency. Officers notice, and it shortens the validation conversation considerably.

Resolving a genuine technical disagreement

Sometimes the contradiction is real: two qualified people reached different conclusions from overlapping evidence.

The honest process has three steps. Get both consultants in the same conversation, which is almost always enough on its own, because most apparent disagreements turn out to be different baselines or different assumptions rather than different opinions. Agree the common inputs in writing: the site area, the scheme revision, the survey dates, the policy standard applied. Then ask each to re-express their conclusion against the agreed inputs.

What survives that process is a real disagreement, and it needs to be reported rather than hidden. A submission that says two assessments reached different conclusions, explains why, and sets out which the applicant relies on and on what basis, is a defensible document. A submission that includes both conclusions without comment is not.

You cannot resolve it by instructing a consultant to change a professional conclusion. The RTPI Code of Professional Conduct, the RICS Rules of Conduct and the equivalent codes for ecologists, acousticians and engineers all prevent a member from stating something they do not believe. An instruction to amend a conclusion puts the consultant in breach and puts you in a worse position than the original contradiction.

Who arbitrates

The client decides what the application relies on. Each consultant remains responsible for their own opinion. Those two statements sit together uncomfortably but they are both true.

In practice the project manager or planning consultant coordinates: they identify the inconsistency, convene the discussion, record the agreed inputs, and decide what goes in the submission. Where a conclusion cannot be reconciled, the options are to commission an independent review, to drop reliance on one of the reports, or to submit both with an explanation.

An independent review is worth it where the disputed point is decisive and the scheme is large. It is disproportionate on a householder application. The professional directory is one route to a reviewer with the right competence for a specialist report, and a review that confirms one position closes the argument faster than another round of correspondence.

Where the disagreement is with the authority's own adviser rather than between your consultants, the position is different and the approach set out in what to do when the council's expert disagrees with your consultant applies instead.

What the officer does when they spot it

Four responses, in increasing order of damage.

A validation query, which is the best outcome: the application is held, you supply a corrected document or a clarification note, and the clock starts again.

A request for clarification during determination, which costs you a week or two and leaves a record on the public file that a document was inconsistent.

Reduced weight, which is the quiet one. The officer accepts the application, decides they cannot rely on the inconsistent evidence, and assesses that issue on their own judgement or on the consultee's view instead. You never find out this happened unless you read the officer's report carefully.

Refusal for inadequate information, where the inconsistency goes to something central and the authority cannot assess the application without resolving it. This is uncommon but it happens, and it is difficult to appeal because the Inspector will usually agree that the evidence was unclear.

Consultees spot contradictions too, and they are often better at it than officers because they read one document closely rather than twenty quickly. A lead local flood authority comparing your impermeable area figure with the drawing will notice.

Withdrawing and resubmitting

Decide between an addendum and a resubmission on one question: does the corrected document change the conclusions, or only the figures leading to them.

Where the conclusions hold, submit a short addendum or errata note identifying the error, giving the corrected figure, and confirming that the conclusions are unaffected. Keep it to a page. Reissue the full report only if that makes it easier to read.

Where the conclusions change, reissue the report with a new revision and a clear change log, and write to the officer explaining what changed and why. Expect re-consultation on the point, and expect the determination period to be extended.

Withdrawal and resubmission is right only where the scheme itself has changed materially, and it carries a new fee unless a fee concession applies. Before withdrawing, ask the officer: many will prefer an amended document on the existing application to a fresh one, because it keeps their performance statistics intact.

A reconciliation checklist

Run this before every submission:

1. One source of truth for the schedule of accommodation, held by one named person.
2. Every technical report names the drawing number and revision it assessed.
3. The consistency matrix completed and attached as a schedule.
4. Survey dates listed with a statement of validity for each.
5. Area measurements all stated as gross internal or gross external, consistently.
6. Levels all on the same datum, stated.
7. A single reference system for trees, windows, plots and phases across every document.
8. A final read of the planning statement against each technical summary, by someone who did not write either.

That last item finds more errors than the rest combined, because the planning statement is where every number gets repeated and it is usually written last and fastest. Keep the Planning Statement as the document that cites the others rather than the document that restates them, and the restatement errors disappear.

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.