Sequential Test Update 2025: Surface Water Flood Risk Changes Explained

The previous approach to surface water flooding

Prior to 2022, the Sequential Test was generally considered to apply to sites at risk of flooding from rivers and the sea. Surface water flooding, which occurs when rainfall exceeds the capacity of natural or engineered drainage systems, was dealt with separately through drainage strategies and SuDS proposals submitted with the planning application. This was a logical position, because development inevitably changes how surface water moves across a site, through the introduction of impermeable surfaces, changes to run-off rates and alterations to ground levels.

In 2022, the Government updated the National Planning Practice Guidance (NPPG) to require the Sequential Test to consider all sources of flooding. From that point, surface water flooding, regardless of how local or minor, was treated in the same manner as flooding from rivers and the sea. A planning application on a site affected by surface water flooding therefore had to be supported by a Sequential Test.

The impact of the December 2024 surface water maps

The Environment Agency’s (EA) mapping indicates where surface water flooding is likely to occur. Although the maps are intended as an indication of likely areas of risk, they are relied upon definitively by Local Planning Authorities in determining applications.

In December 2024, the EA published updated surface water flood maps. The new mapping draws on improved topography and hydraulic modelling and significantly expanded the areas of England identified as being at risk from surface water flooding. The practical effect was that many more sites were caught by the surface water layer, and therefore by the requirement to provide a Sequential Test.

The revised National Planning Policy Framework was published in the same month. It retained the all-sources approach, with paragraph 175 providing an exemption only where a site-specific Flood Risk Assessment could demonstrate that no built development would be located on any area at risk from any source, now or in the future. In all other cases, a Sequential Test was required, even where the risk of flooding could be mitigated through the design of the development.

The position became binary and inflexible. The Sequential Test had become a significant procedural obstacle to development, including on small infill and brownfield sites where the mapped surface water risk was localised and could be designed out.

The September 2025 update: a proportionate approach

The NPPG on flood risk and coastal change was updated in September 2025 in respect of the Sequential Test, and specifically in relation to surface water flooding. Paragraph 027 now states:

“In applying paragraph 175 a proportionate approach should be taken. Where a site-specific flood risk assessment demonstrates clearly that the proposed layout, design, and mitigation measures would ensure that occupiers and users would remain safe from current and future surface water flood risk for the lifetime of the development (therefore addressing the risks identified e.g. by Environment Agency flood risk mapping), without increasing flood risk elsewhere, then the sequential test need not be applied.”

Planning Practice Guidance, Paragraph 027 (Reference ID: 7-027)

What this means for development

Subject to a site-specific Flood Risk Assessment demonstrating that the proposal does not increase flood risk elsewhere, and that occupiers and users will remain safe for the lifetime of the development, there is no longer a requirement to submit a Sequential Test on sites affected by surface water flooding alone. This is a welcome and proportionate change. It will unlock development on sites that have been held up by this issue, and reflects a practical approach where mitigation is proposed and implemented appropriately. It allows surface water flood risk to be suitably managed through sustainable drainage.

The limits of the proportionate approach

It is important to be clear about the scope of the September 2025 update. The proportionate approach in paragraph 027 is specific to surface water flooding.

The exemption applies to surface water flooding only. It does not extend to rivers, the sea, groundwater, sewers, reservoirs or any other source. The Environment Agency’s Standing Advice is explicit on this point.

Where a site is in Flood Zone 2 or 3, or shows risk from any source other than surface water, the Sequential Test continues to apply in the usual way. The September 2025 update also does not reduce the requirement for a robust, site-specific Flood Risk Assessment. The FRA is the document on which reliance is placed to disapply the Sequential Test, and it must demonstrate clearly, on the evidence, that the development will be safe for its lifetime, that climate change uplifts to rainfall intensity have been applied, and that surface water is not displaced onto neighbouring land.