Sub-consultants and where liability sits

A sub consultant liability planning report question usually arrives late, when something has gone wrong and everybody wants to know whose problem it is. The short answer is that liability follows the contract, not the letterhead. If you appointed a consultancy and that consultancy sub-contracted the acoustic modelling to somebody else, your claim is against the consultancy you appointed, and their claim is against their sub-consultant.

That is tidy in theory. It stops being tidy when the sub-consultant is the one with the specialist insurance and the head consultant is a two-person practice.

How a report can have several authors

A planning technical report frequently combines work from more than one discipline, and the combination is invisible on the cover.

An environmental statement chapter on air quality may rest on traffic data produced by a transport consultant and dispersion modelling run by a third party. A biodiversity net gain assessment may use habitat survey data from a seasonal subcontractor and a metric calculation done in-house. A flood risk assessment may include hydraulic modelling bought in from a specialist. A structural appraisal may rely on laboratory testing of samples, which is itself a separate appointment.

None of that is improper. It is how technical work gets done. The problem arises when the document does not say who did what, so nobody can tell where a finding came from or who stands behind it.

Direct appointment against sub-consultancy

You have two structures, and the choice has consequences.

Under direct appointment you contract separately with each specialist. You get a direct claim against each, you see their insurance, and you can choose the individuals. You also take on the coordination risk, because when the acoustician's assumptions do not match the transport consultant's traffic figures, it is your job to notice.

Under sub-consultancy you contract with one lead consultant who takes responsibility for the whole deliverable and appoints the others. Coordination becomes their problem and their liability covers the entire output. You lose visibility of who is doing the work and you lose any direct route against the specialist.

For most schemes, single-point responsibility is worth more than visibility, provided the lead consultant is substantial enough to stand behind it. Where the lead is small and the specialist work is the expensive part, direct appointment of the specialist often makes more sense.

Collateral warranties and third party rights

Where you want a claim against somebody you did not appoint, there are two mechanisms.

A collateral warranty is a separate contract between the sub-consultant and you, giving you a direct right to sue them for breach of their duty of care. It is the traditional route and it needs to be signed, which means asking for it at the point the sub-consultant is appointed rather than after completion.

Third party rights under the Contracts (Rights of Third Parties) Act 1999 achieve a similar effect by naming you in the sub-consultancy agreement as a person entitled to enforce its terms. It is quicker, because nothing separate has to be executed, and it is now common in construction documents.

Either way, read the limits. Most warranties cap liability, exclude consequential loss, limit the number of assignments and include a net contribution clause, which means the sub-consultant only pays their share of a loss rather than the whole of it where others also contributed. A net contribution clause in a chain of consultants can leave a claimant recovering a fraction of their loss.

Novation to a contractor

On design and build projects, consultant appointments are often novated to the contractor at the point the building contract is signed. The consultant then owes their duties to the contractor rather than to you.

For planning documents this creates a specific oddity. The planning consultant and the technical specialists produced evidence the authority relied on when granting permission, but after novation their client is the contractor, whose interests during construction may not match yours. If a condition then needs discharging on terms that suit the build programme rather than the scheme, you are no longer the client instructing on it.

Keep planning-stage appointments out of the novation where you can, or take a collateral warranty from the consultants in your favour before novation happens. Retaining the planning consultant directly, even on a small retainer, usually pays for itself during the condition discharge period.

Insurance following the chain

Professional indemnity cover is the thing that actually matters, because a liability against an uninsured party is a paper right.

Three checks on any technical consultant, whether direct or sub. That the policy covers the specific discipline, because several disciplines are excluded or separately rated. That the limit of indemnity is appropriate for the scheme, and whether it is per claim or in the aggregate, since an aggregate limit shared across a practice's whole year may be exhausted before your claim arrives. And that the cover will be maintained for a period after completion, because these policies are written on a claims-made basis and a lapsed policy means no cover for a historic report.

Ask for the certificate, not a statement. And ask again at renewal on a long project.

Some disciplines carry exclusions that surprise people. Cover for contamination and pollution work is often carved out or limited, and cover for fire safety advice has become harder to obtain and more heavily restricted since 2017. Where you are relying on a fire engineer's work for a Fire Statement, check the position specifically, because a legally required professional with a restricted policy is a risk worth knowing about before you submit.

Naming the author in the document

Several professional standards require the author to be identified and their competence stated, and it is good practice everywhere else.

A properly constructed report carries a title page or a quality control sheet naming the person who wrote it, the person who checked it, the person who authorised it, their qualifications and memberships, and the date of each. Where a section was produced by a different organisation, that organisation and the section it produced should be named in the same place.

This matters beyond liability. An authority assessing whether a report was prepared by a competent person cannot do so if the document is anonymous, and for the report types where a licensed or competent professional is legally required, an unnamed author invites a request for further information. Our note on viability assessment competence and RICS standards covers one discipline where the naming requirement is explicit, and accredited testing and why laboratory choice matters covers the case where the sub-contracted element is a laboratory rather than a consultant.

Setting the appointment up properly

Do this at appointment, when you have bargaining power, rather than at claim, when you have none.

1. Ask in the tender whether any part of the work will be sub-contracted, and to whom.
2. Require prior written consent for any sub-contracting not disclosed at tender.
3. Require third party rights or a collateral warranty from any sub-consultant whose work is material.
4. Obtain insurance certificates for both the lead and the material sub-consultants, with the limit and the basis stated.
5. Agree that the report will name the author, checker and authoriser for each section, including sub-contracted sections.
6. Agree who owns the underlying data and models, because you will want them if you change consultant.

That last point is the practical one people forget. A hydraulic model, a noise model or a metric calculation is worth far more than the report, and an appointment that only licenses the report leaves you starting again if the relationship ends.

PlanScope's professional directory is the route for requesting review and sign-off of an AI-assisted draft, and the review request flow records who reviewed what and when. Reports drafted on PlanScope should be reviewed before submission, and for several report types a licensed or competent professional is legally required rather than merely advisable.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice. For specialist technical reports, qualified professional input may be required.