Who prepares a flood sequential test and how it is judged

Nobody needs a licence to write a flood sequential test. There is no statutory competence requirement, no register, no chartered title that the planning system insists on, and a landowner can prepare one themselves. What decides whether it is accepted is the quality of the evidence and the reasonableness of the area of search, and the person judging both is a planning officer rather than a flood specialist.

That is the single most useful thing a self-builder can know about who prepares a sequential test. The document is a planning argument supported by data, not a hydraulic calculation.

No licence applies, and what follows from that

Compare this with the regimes that do impose competence. A protected species licence application has to come from a suitably licensed ecologist. The statutory biodiversity metric expects a competent person. An Environmental Statement must be prepared by competent experts under the 2017 EIA Regulations. The sequential test sits outside all of that.

What good practice looks like instead is a planning consultant or a flood risk consultant with chartered standing in a relevant institution, working to a scope agreed with the authority. Chartered membership of a body such as the Chartered Institution of Water and Environmental Management signals familiarity with the policy, and it carries no legal weight for this document. The weight comes from the method section.

One consequence matters for small applicants. Because anyone may write it, plenty of submitted tests are a page and a half asserting that no alternative sites exist. Those get rejected, and the rejection costs the whole determination period.

When the test is not required at all

Check this before paying for anything. The Planning Practice Guidance on flood risk and coastal change excludes several categories from the sequential test, and a surprising number of self-build and householder proposals fall inside the exclusions.

• Minor development, which the guidance describes as including householder development within the curtilage of an existing dwelling, non-residential extensions with a footprint below 250 m2, and physical alterations that do not increase the size of a building.
• Changes of use, except to a caravan, camping or chalet site, or to a mobile home or park home site.
• Development on a site allocated in the development plan where the sequential test was applied at the plan-making stage, so the test does not need repeating for the same development.

A new separate dwelling is not minor development, whatever its size. So a single self-build plot in Flood Zone 3a attracts the full test, while a two storey rear extension on the house next door does not. That asymmetry catches people out constantly.

What the authority is actually judging

Four things, in this order.

The fourth row is where most tests are thin. Saying a site is unavailable is an assertion. Saying it has an extant permission that has already been started on site, or that it is in three ownerships with no agreement, or that it was marketed for eighteen months without an offer, is evidence. Attach what you relied on.

Vulnerability classification is the row that gets skipped, and it changes the answer. A dwelling is more vulnerable. A shop is less vulnerable. Essential infrastructure and water compatible development sit in their own categories, and the policy consequence in each flood zone differs, which is why the classification belongs in the first paragraph of the Sequential Test (Flood Risk) rather than buried in an appendix.

Where the Environment Agency does and does not comment

This is the misunderstanding that wastes the most time. The Environment Agency is a statutory consultee on development in Flood Zones 2 and 3 and comments on the flood risk evidence, the modelling, finished floor levels, safe access and the flood resistance and resilience measures. It does not carry out the sequential test and does not advise on whether it has been passed.

The sequential test is for the local planning authority to apply, because only the authority holds the land availability evidence for its own area and only the authority can weigh the planning balance. The Agency publishes standing advice and flood risk assessment guidance for applicants, and the sequential test is outside its remit in both.

For surface water on major development the lead local flood authority is the statutory consultee, and it will scrutinise the drainage strategy rather than the site selection. So three bodies look at a flood application and only one of them is judging your search area. The technical work goes in the Flood Risk Assessment, and the comparison of a hydrologist and a drainage engineer sets out who to appoint for that part.

Defining the area of search so it survives scrutiny

The guidance says the area over which the test applies depends on the nature of the proposal and should be agreed with the authority. For a single dwelling that usually means the settlement rather than the whole district, on the basis that the development being proposed is a house in that village rather than a house anywhere in the authority.

Make the argument explicitly. Set out why the development has a geographical requirement, if it has one, and what that requirement is. A replacement dwelling on an existing footprint, an agricultural worker's dwelling tied to a holding, or an extension of an existing business each carry a locational logic that a speculative plot does not.

And write the assumption down. Where the authority will not confirm the search area at pre-application stage, state the area you have used, state why, and invite the officer to tell you if they disagree before determination. An officer who refuses on search area grounds having never engaged with a stated assumption is in a weaker position on appeal.

Why tests get rejected

Six reasons account for most of it.

1. Search area too narrow, usually drawn around the applicant's own landholding.
2. Site list drawn only from the local plan allocations, ignoring the brownfield register and windfall sites.
3. Availability conclusions with no supporting evidence.
4. Suitability dismissed on grounds that would also rule out the application site.
5. No sequential approach within the site, so the dwelling sits on the lowest ground.
6. The vulnerability classification omitted or wrong.

Where the author also stands to gain from the outcome, the authority reads the availability conclusions more sceptically, and the general points about a conflict of interest in a technical report apply here with force. Declare the relationship rather than leaving it to be discovered.

Appointing alongside the flood risk work

Commission the sequential test and the flood risk assessment together, from the same adviser where possible, because the vulnerability classification and the modelled levels feed both. Then agree four things in writing before work starts: the search area, the number of candidate sites in scope, whether the exception test is included, and who prepares the flood warning and evacuation plan.

For a single plot, a realistic package is a short test across the settlement with a schedule of perhaps six to twelve candidate sites, a site layout drawing showing the sequential approach within the plot, and the flood risk assessment itself. Where the modelling has to go beyond the Agency's published outputs, that is a separate instruction with a separate fee.

Review before submission is where a weak test gets caught. PlanScope's professional directory is the route to a reviewer who can look at the flood work and sign off a draft, and an AI-assisted draft is a starting point for that reviewer rather than a substitute for them. This is general guidance, not legal advice, so 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. For specialist technical reports, qualified professional input may be required.