ClientEarth (No.2) v Secretary of State for the Environment, Food and Rural Affairs

Article 23 of Directive 2008/50/EC imposes a narrow and greatly constrained discretion when an air quality plan is required. The Secretary of State must aim for compliance by the soonest possible date and select a route that reduces exposure as quickly as possible. Measures must make compliance likely, not merely possible. Cost may inform the choice between equally effective measures, but cannot justify a later compliance date or a slower route. Proportionality permits no more than is required to achieve compliance. A plan based on routine modelling intervals, administrative convenience, or markedly optimistic emissions assumptions is unlawful where those features prevent identification of the quickest effective route.

ClientEarth sought judicial review of the Government’s 2015 Air Quality Plan for nitrogen dioxide. The challenge followed earlier proceedings in which the Supreme Court declared the United Kingdom in breach of Article 13 of Directive 2008/50/EC and required a new plan. ClientEarth argued that the new plan failed to comply with Article 23(1) of the Directive and regulation 26(2) of the Air Quality Standards Regulations 2010.

The central issues were whether the plan pursued compliance within the shortest possible time, whether its modelling assumptions were lawful, and whether it sufficiently assessed alternative measures.

1. Claim allowed. The 2015 Air Quality Plan was declared non-compliant with Article 23(1) of Directive 2008/50/EC and regulation 26(2) of the Air Quality Standards Regulations 2010, and was quashed.
2. Article 23 imposes a mandatory obligation of result. Although a Member State retains some discretion in selecting measures, that discretion is narrow and greatly constrained. The plan must pursue compliance by the soonest possible date, reduce exposure as quickly as possible, and include measures making compliance likely rather than merely possible. The court applied the limits on administrative discretion identified in Dieter Janecek v Freistaat Bayern [2008] ECR I-6221.
3. Cost may be considered when choosing between equally effective measures or allocating responsibility for payment. It cannot determine the compliance date or justify choosing a slower route where another route produces results more quickly. Proportionality means doing no more than is required to meet the target.
4. The use of five-year modelling intervals had become determinative of the 2020 target, rather than being justified by an assessment of the earliest achievable date. The Secretary of State should have identified the quickest measures, assessed when they could be introduced, and modelled their likely effect. The resulting error tainted the exercise.
5. The plan also relied on markedly optimistic assumptions about emissions from Euro 6 diesel vehicles, despite emerging evidence that real-world emissions were substantially higher. It therefore identified measures which might achieve compliance only if the optimistic assumptions proved correct, contrary to the requirement that compliance be likely.
6. Further questions about the number and scope of clean air zones, alternative measures, funding and London-specific provisions were left for reconsideration after fresh modelling.

The judgment records earlier judicial review proceedings concerning previous air quality plans. The Supreme Court declared the United Kingdom in breach of Article 13 of Directive 2008/50/EC in [2015] UKSC 28 and required national-court enforcement. Those decisions formed the background to the present first-instance claim.