Flood risk: Sequential testing should not be an afterthought

As the draft National Planning Policy Framework (NPPF) in the UK is due to be finalised, subject to government delays following the number of responses received during consultation period - different types of land, or potential sites for development, will be put back on the table to meet the housing demands for local authorities. The proposed increase in housing targets will place pressure on local authorities to consider sites, including greenfield sites, that were previously not viable or not deemed necessary from a planning perspective. Although this provides an opportunity for landowners and developers, the usual viability tests will still have to be applied. Daniel Watson, technical director of hydrology & hydrogeology at SLR discusses.

As built environment professionals begin to consider potential sites that through the proposed changes to the NPPF are now considered acceptable in planning terms, there are still potential restrictions that cannot be overlooked.

One significant limitation is the sequential test for flood risk, the wording for which remains unchanged in the draft NPPF. Paragraph 168 requires that “development should not be allocated or permitted if there are reasonably available sites appropriate for the proposed development in areas with a lower risk of flooding”. The sequential test is about adopting a precautionary approach to managing flood risk and in particular enforcing the principle that the most sustainable means of achieving this is through avoidance, i.e. to direct development away from higher risk areas.

Understanding the requirements of sequential testing

It is the responsibility of the applicant to provide evidence to the Local Planning Authority that a development passes the test. This is however not necessary if a site has been allocated in the Local Plan process as it will have already been sequentially tested as part of the Call for Sites and Stage 2 and 3 Sustainability Appraisal process (to achieve allocation). As a result, once a specific site is allocated, it can be presumed that it passes the sequential test.

For sites that are not allocated sequential testing cannot be an afterthought in the planning process as it is a potentially blunt tool with a binary outcome. If the sequential test cannot be passed, then the application will be refused. It is recommended that if a site is at risk, or partially at risk of flooding, the parameters that should be applied to the sequential test should be agreed in writing with the Local Planning Authority at an early stage and if necessary, works should be undertaken to confirm if the site will pass. This should ideally occur before significant resources are devoted to preparing an application. Clearly the pre-application process is an ideal means of engaging with Council Officers in this respect.

If consultation with the Local Planning Authority confirms that a formal sequential test is required, then a list of alternative competing sites will need to be compiled. This list will typically be comprised of sites already identified for development (i.e. allocated land), sites which were safeguarded for future development within the Local Plan process, sites which were taken through the Call for Sites, other land on the brownfield land register and finally any other sites that are actively being marketed for sale.

This list of competing sites is then reviewed to screen out land that is subject to higher levels of flood risk and also any land that is not reasonable available for the development being considered. When defining the term ‘reasonably available’, consideration is given to suitability, availability and (to a lesser extent) viability.

It is important to note that it is not possible to guarantee the outcome of this process and that the review process may identify a site which is sequentially preferable. If this occurs there is little or no potential for a successful planning application unless circumstances change.

Areas of possible confusion in sequential testing

Whilst the intention of the sequential test is arguably clear, there is much potential ambiguity in its application given the range of development types and geographic spread it covers. We have noticed significant variation in its interpretation by individual Local Planning Authorities and planning officers. This inevitably leads to a degree of confusion.

Some areas of confusion and ambiguity have however been clarified by planning appeals and high court decisions. Whilst it is possible that individual Local Planning Authorities and planning officers may continue to apply the test differently, these decisions (discussed below) provide a useful guide as to how the test should be applied in these areas.

What flood risk

When originally implemented, the sequential test was often applied just in relation to fluvial and tidal flooding as shown by the Flood Map for Planning. There was also no mention of climate change in the original wording of the test.

Subsequent updates to the NPPF have broadened the scope of the sequential test such that all sources of flood risk have to be considered and changes to flood risk as a result of climate change are also a material consideration. For instance, the sequential test must now be applied even if the site is only at risk of surface water flooding.

This requirement was tested and confirmed as a part of the appeal for development at Land between 8 & 10 Meadow Close [1].

Site size

When identifying potential alternative sites for consideration as a part of a sequential test, it is required that developers consider site of different sizes and not just alternative sites of a comparable size / capacity. This might include parts of a larger site or a combination of smaller sites which could accommodate a disaggregation of the proposed development.

This requirement is set out in the planning practice guide and was confirmed as part of the Mead/Redrow High Court Judgement [2].

The red line boundary and flood risk

The sequential test should be applied to the whole of a development not just the part of the site to be occupied by dwellings / buildings. Therefore, if important aspects of the scheme such as access roads and parking areas are proposed in areas of elevated risk, then the sequential test must be applied.

This requirement is not clearly set out in current planning guidance but was a key reason for the dismissal of the appeal for development at Land at Little Bushey Lane [3].

While not explicitly addressed by the planning appeal, Environment Agency guidance states that “the sequential test may not need to be applied if the development is laid out so that only elements such as public open space, biodiversity and amenity are at risk of flooding”. Based on this we would argue it is reasonable to assume any aspect of development that is frequently provided offsite, and in that instance secured through separate legal agreement, should be ignored when applying the sequential test. This remains however an area of uncertainty.

Looking ahead

The draft NPPF signals exciting opportunities for development, but also reinforces the importance of sound planning principles, especially concerning flood risk. The sequential test remains a crucial element in this process, ensuring that new developments are safe, sustainable, and well-suited to their environment. For developers, understanding and applying the test correctly is not just a regulatory hurdle — it is a fundamental part of responsible development in an era of increasing climate uncertainty. As planning pressures mount, the sequential test is a key safeguard that should be approached with diligence and care, ensuring new homes are built in the safest possible locations.

Just because a piece of land might be released for development that has previously been safeguarded, if it is at risk of flooding, it does not follow that it will necessarily pass the sequential test.

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References

[1] https://acp.planninginspectorate.gov.uk/ViewCase.aspx?caseid=3314268

[2] https://assets.publishing.service.gov.uk/media/66012fd165ca2fc1fa7da734/9_Mead_Realisations_Limited_v_Secretary_of_State_for_Levelling_Up__Housing_and_Communities__2024__EWHC_279__Admin_.pdf

[3] https://acp.planninginspectorate.gov.uk/ViewCase.aspx?caseid=3314268