Court of Appeal Upholds Decision on Project Separability and Staged Environmental Assessments in Sizewell C Case

Citation: [2023] EWCA Civ 1517
Judgment on


In the notable case of Together Against Sizewell C Limited, R (on the application of) v Secretary of State for Energy Security and Net Zero, the Court of Appeal (Civil Division) addressed key legal principles relating to “appropriate assessment” under the Habitats Regulations, project separability, and the staged approach to environmental assessments. This case presents significant guidance on how decision-makers should regard interconnected projects concerning environmental impact assessments, especially in the planning context of nationally significant infrastructure projects.

Key Facts

The appellant, Together Against Sizewell C Limited (TASC), challenged the Secretary of State’s decision to grant a development consent order for Sizewell C nuclear power station, arguing that it erred in law by not including the permanent supply of potable water as part of the project’s “appropriate assessment” under Regulation 63 of the Habitats Regulations. The Secretary of State differentiated between the construction of the power station and the supply of potable water as separate projects, the latter being inchoate and left to be addressed in the future by Northumbrian Water Limited’s (NWL) water resources management plan (WRMP24).

Project Separability and “Appropriate Assessment”

The court reinforced the principle that decision-makers possess the discretion to determine the nature and extent of a “project” under the Habitats Regulations, applying conventional Wednesbury principles to evaluate the reasonableness of such determinations ([Bowen-West v Secretary of State for Communities and Local Government (2012)]([2012] Env. L.R. 22) and [Ashchurch Parish Council v Tewksbury Borough Council ([2023] PTSR 1377]).

The “Staged Approach” to Assessment

Endorsing a “staged approach” to environmental assessment, the court accepted this method as legitimate to prevent what has been labelled “sclerosis in the planning system” ([Forest of Dean (Friends of the Earth)) v Forest of Dean District Council [2015] PTSR 1460]). This approach allows for the consideration of cumulative effects to be deferred to a subsequent stage when those effects are sufficiently identifiable.

Non-Salami Slicing

The court drew a distinction between cases of “salami-slicing” or “project-splitting” to avoid assessment and cases where separate assessments are warranted due to the inchoate nature of one of the projects. The court rejected the notion that every aspect of potential future connected projects has to be definitively assessed before any can progress, asserting instead that projects can be treated as separate and assessed accordingly per their own development and consent stages.

An essential legal aspect considered was the statutory duty of utility companies under relevant legislation like the Water Industry Act 1991, which the court found influential in determining whether projects related to such utilities should be treated as separate from the primary development.


The appeal was dismissed on the grounds that the Secretary of State made no error in determining that the permanent supply of potable water to the power station was a separate project and in choosing to defer the assessment of its environmental impact to a later stage. This means the decision to grant development consent for the nuclear power station stood, notwithstanding the ongoing assessment and eventual determination of the water supply issue.


The ruling confirms the court’s endorsement of a wider discretion afforded to decision-makers in determining the nature and extent of a project for the purposes of the Habitats Regulations. It upholds the “staged approach” for assessing interconnected, but separate, projects. The decision exemplifies a pragmatic approach to environmental assessment, allowing nationally significant infrastructure projects to proceed without delay, while ensuring that future projects with potential cumulative environmental impacts will still undergo rigorous assessments at the appropriate stage.

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