Boswell v Secretary of State for Energy Security and Net Zero: The Role of NPS Policy in Assessing and Weighing GHG Emissions in NSIP Decisions

Introduction

This commentary examines the Court of Appeal’s decision in Boswell, R (On the Application Of) v Secretary of State for Energy Security and Net Zero ([2025] EWCA Civ 669). At issue was whether the Secretary of State lawfully assessed the significance of greenhouse gas (GHG) emissions from a proposed gas-fired electricity station with carbon capture and storage (CCS/CCUS) under the Planning Act 2008 and the Infrastructure Planning (Environmental Impact Assessment) Regulations 2017. Dr Andrew Boswell challenged three aspects of the decision: (1) reliance on IEMA guidance; (2) the effect of National Policy Statement EN-1 paragraph 5.2.2 on EIA significance and weight in the planning balance; and (3) adequacy of the “reasoned conclusion” on GHG emissions. The Court dismissed the appeal, clarifying the interplay between policy, EIA, and planning judgment.

Summary of the Judgment

The Court of Appeal upheld the Secretary of State’s grant of a development consent order for the Teesside power station with CCUS. Key holdings:

• No error in using the NPS policy (EN-1 and EN-2) to determine that GHG emissions were a “significant adverse effect” for EIA purposes and to give them significant negative weight in the planning balance.
• The IEMA guidance remains advisory for practitioners; it is not binding policy, and decision-makers have discretion in how they reach and explain “significance.” Neither the Examining Authority nor the Secretary of State applied the IEMA significance criteria (section 6.3) in their decisions.
• The Secretary of State gave legally adequate reasons under section 116 of the Planning Act 2008 and regulations 21 and 30 of the 2017 Regulations. There was no failure to “benchmark” or “contextualise” beyond what the NPS provided and the decision-maker’s judgment allowed.
• National policy can legitimately guide both the assessment of significance within an EIA and the weight given to that significance in the planning balance.

Analysis

1. Precedents Cited

• Frack Free Balcombe Residents’ Association v SS for Housing... [2025] EWCA Civ 495: Courts may not re-open merits of energy policy or climate objectives.
• R (Friends of the Earth) v Heathrow Airport [2020] UKSC 52: Structure and purpose of the Planning Act 2008 and NSIPs.
• R (Scarisbrick) v SSCLG [2017] EWCA Civ 787 & R (ClientEarth) v SSBIS [2021] EWCA Civ 43: Principles for interpreting and applying National Policy Statements.
• R (The Law Society) v Lord Chancellor [2018] EWHC 2094 (Admin): Flawed logic as irrationality in public law.
• South Bucks DC v Porter (No. 2) [2004] UKHL 33: Legal requirements for “adequate reasons.”
• R (Goesa) v Eastleigh [2022] EWHC 1221 & R (Boswell) v SSoT for Transport [2024] EWCA Civ 145: Flexibility in EIA methodology and judgment.
• R (Finch) v Surrey CC [2024] UKSC 20: Scope of EIA obligations distinct from planning merits; distinguished on facts.

2. Legal Reasoning

The Court emphasized its narrow judicial review role: to determine legality, not merits, of the Secretary of State’s decision. It reaffirmed:

• Policy primacy under section 104 PA 2008: Applications must be decided in accordance with NPSs. Where benefits outweigh harms (section 104(7)), an NSIP may be consented.
• EIA requirements (Regulations 21 & 30): Decision-makers must examine environmental information, reach a reasoned conclusion on significant effects, integrate that into their decision, and, if granting consent, consider monitoring. The adequacy of reasons aligns with section 116 PA 2008 and South Bucks.
• NPS policy on GHG emissions (EN-1 para 5.2.2; EN-2 para 2.5.2): Acknowledges that CO₂ emissions from some energy infrastructure are “significant adverse impacts” but not grounds to prohibit projects due to overarching need and other decarbonisation measures (e.g. ETS).
• Role of IEMA guidance: A practitioner’s tool offering methodological options; not adopted as binding policy. The Court found no evidence that the Secretary of State applied the IEMA significance criteria in section 6.3.
• Significance vs weight: The Court rejected a rigid separation between EIA significance assessment and planning-balance weight. The NPS guidance can inform both stages without predetermining outcomes or curtailing EIA scope.

3. Impact

This decision provides clarity on several points:

• Discretion in EIA and planning judgment: Decision-makers retain latitude in defining “significance” and weighing effects, subject to giving adequate reasons and respecting NPS policy.
• Limits of advisory guidance: External guidance documents (e.g. IEMA) remain advisory unless formally adopted in policy; courts will not imply binding status.
• Integrated approach to policy and EIA: National Policy Statements may legitimately set out significance principles that guide both the environmental assessment and the planning balance.
• Restraint against merits review: Parties cannot use judicial review to re-argue planning merits or attack NPS content indirectly; the focus remains on legality and procedural fairness.

Complex Concepts Simplified

• Nationally Significant Infrastructure Project (NSIP): A large-scale development (power stations, pipelines) requiring a development consent order under the Planning Act 2008.
• National Policy Statement (NPS): A document setting national policy and presumption in favor of certain types of NSIPs. Section 104 requires decisions to accord with NPSs.
• Environmental Impact Assessment (EIA): A process to identify, describe, and assess significant environmental effects. Regulations 21 and 30 require a “reasoned conclusion” on significance.
• Significance of GHG emissions: A qualitative and quantitative judgment about whether emissions pose a “significant adverse impact” on climate.
• IEMA guidance: Voluntary best-practice guide for practitioners on GHG assessment; not binding policy.
• Planning Balance: Weighing of benefits against harms (including environmental impacts) when deciding to grant consent under section 104(7).

Conclusion

Boswell v SS for Energy Security and Net Zero reaffirms that Secretaries of State and Examining Authorities enjoy broad discretion in assessing the significance of environmental impacts and determining their weight in the planning balance, so long as they comply with procedural requirements and give adequate reasons. It clarifies that National Policy Statements may legitimately guide both steps—environmental assessment significance and planning-balance weight—and underscores that advisory documents like the IEMA guidance do not bind decision-makers. The judgment strengthens legal certainty for future NSIP decisions by delineating the boundary between policy guidance, procedural fairness, and substantive planning discretion.