Sequential Test: agreeing the area of search

The area of search decides the outcome of a flood risk sequential test more often than the flood zone does. Draw it too wide and you inherit dozens of sites you have to discount one by one. Draw it too narrowly and the officer rejects the test as self-serving, usually in the last fortnight of the determination period.

The default is the local planning authority's administrative area. Departing from that default is possible, and sometimes correct, but it has to be argued from the development's function rather than from convenience.

Why the geography decides the result

The sequential test asks whether there are reasonably available sites appropriate for the proposed development in areas at lower risk of flooding. If there are, permission should be refused. The test is comparative, so the comparison set is the whole argument.

Since the December 2023 revision, the test applies to all sources of flood risk rather than river and sea flooding alone. Surface water, groundwater, reservoirs and sewer flooding all count. That change widened the number of sites that fail and it also widened the evidence you need about the alternatives, because a candidate site in Flood Zone 1 with a surface water flow path across it is not automatically at lower risk.

Officers who reject a sequential test almost always reject it for one of three reasons: the search area was too small, the discount reasons were unsupported, or the test ignored sites the council's own evidence base identifies. The first is the one applicants control least well.

Setting the geography against the need

Start from what the development is actually for, then define the smallest area that meets that need honestly.

The reasoning has to be published somewhere the council accepts. A housing needs survey, an adopted local plan policy that identifies a settlement hierarchy, an economic needs assessment, or a school place planning report all do the job. An assertion by the applicant does not.

Where you are arguing for a smaller area, expect the council to test it. The question they ask is whether the need could be met somewhere else without material disadvantage, and a good answer names the disadvantage rather than asserting one.

What makes a site reasonably available

Available means available now, or within a timescale that meets the need. A site with an extant permission for something else, a site in an unwilling owner's hands, and a site that is physically constrained by ownership severance are all arguable discounts, provided you evidence them.

The Planning Practice Guidance on flood risk and coastal change points to the council's own evidence base as the starting point. In practice that means the strategic housing and economic land availability assessment, the brownfield land register, the local plan allocations and any call for sites responses that the council has published. Use those lists rather than compiling your own, because compiling your own invites the response that you left something out.

Suitability is separate from availability. A site large enough in principle may be unsuitable because it is allocated for another use, because it lies in the Green Belt, because it carries a heritage designation that would prevent the quantum, or because its own flood risk from a different source is worse. All of those are legitimate discounts when they are evidenced.

Viability is the weakest discount and the one most often challenged. Saying a site is unviable requires the same order of evidence as a viability case in any other context, and a single line in a table will not survive.

Recording the discounts

Build the test as a table with one row per site and four columns: the site reference from the council's own evidence base, its area and capacity, the flood risk position across all sources, and the reason for discount with the evidence relied on.

Do not abbreviate the reasons. "Not available" is not a reason. "Allocated for employment use under policy E3 and subject to a 2024 reserved matters approval for a distribution unit" is a reason, and it can be checked.

Two further disciplines help. Give the date at which the availability position was assessed, because sites move. And include the sites that pass, if any, with an explanation of why the proposal cannot go there. A test that discounts every single alternative on the first pass reads as constructed backwards, and officers notice.

The output belongs in a standalone Sequential Test document cross-referenced from the Flood Risk Assessment rather than buried in an appendix. Officers copy it into the committee report, so make it copyable.

Where the local plan has already applied the test

Where a site was allocated through the plan-making process and the sequential test was applied at that stage, the guidance accepts that it does not normally need to be reapplied for a proposal consistent with the allocation. The practical conditions are that the allocation is current, that the proposal matches what was allocated in use and scale, and that the flood risk evidence has not changed materially since adoption.

That last condition does most of the work now. A plan adopted before the 2023 change to all sources of flood risk may have applied a narrower test, and climate change allowances have been updated since many plans were examined. Check the strategic flood risk assessment that underpinned the allocation and its date before relying on it.

The test is also not required for minor development or for changes of use, with the exception of a change of use to a caravan, camping or chalet site. A site-specific flood risk assessment may still be needed, and the basement flood risk tests apply to below-ground accommodation regardless of the sequential position.

Presenting the test so an officer can adopt it

Case officers are writing a report under time pressure and they need three things from you: a clear statement of the area of search and its justification, a table they can lift, and a conclusion in the language of the policy.

Write the conclusion as a finding, not a plea. Something to the effect that no reasonably available sites appropriate for the development exist in areas at lower risk of flooding within the defined area of search, for the reasons set out in the table. Then deal with what follows. If the proposal is in Flood Zone 2 or 3 and the vulnerability classification requires it, the Exception Test comes next and needs both limbs answered.

Send the draft to the case officer before you submit if the relationship allows it. Agreeing the area of search in advance costs one email and saves a refusal. The lead local flood authority will separately scrutinise the surface water case, and understanding what it checks in a drainage strategy helps keep the two consultations aligned.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and verify the current National Planning Policy Framework policy references on gov.uk, because the Framework moved to policy codes in the edition published on 17 August 2026. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.