Camilla Swire, R (on the application of) v Canterbury City Council

Whether development is likely to have significant environmental effects is an evidence-based planning judgment. The threshold requires more than a bare possibility, but a serious possibility of significant effects is sufficient. A planning authority must obtain information reasonably necessary to make that judgment, but need not assess hypothetical mitigation schemes which are uncertain, unworked-up and incapable of realistic assessment.

Cumulative effects are considered only so far as it is reasonable to do so. A court will intervene under conventional Wednesbury principles only where no reasonable authority could have been satisfied that it had sufficient information. Post-decision evidence may elucidate, but must not fundamentally alter or contradict, the contemporaneous reasons.

The claimant sought judicial review of Canterbury City Council’s grant of planning permission to Barratt David Wilson Homes Kent for a new eastbound A2 slip road and associated works at Wincheap, Canterbury.

The challenge alleged that the Council had unlawfully concluded that the development was not EIA development. In particular, it was said that the Council had failed to assess the loss of park-and-ride capacity, the possible expansion of the park-and-ride facility, and related traffic and air-quality effects. The claimant also challenged reliance on section 278 of the Highways Act 1980 and the adequacy of the information before the Planning Committee.

1. Claim dismissed. The Council’s decision to grant planning permission and its conclusion that a full EIA was unnecessary were lawful and rational.
2. Under the EIA Regulations, the question whether development is likely to have significant effects on the environment requires an evidence-based planning judgment. “Likely” means more than a bare possibility but includes a serious possibility. The decision-maker must have regard to uncertainty and the precautionary principle, and must have sufficient information to evaluate the likely significant effects.
3. The Council was entitled to conclude that the slip road’s effects on park-and-ride capacity, traffic and air quality were not likely to be significant. It could rely on the consultation response from Kent County Council, the transport assessment, the development plan and the financial contribution secured under the section 106 agreement. It was not required to assess every possible future form of park-and-ride expansion, including multi-storey or water-meadow options, because no sufficiently certain or worked-up scheme existed.
4. The Council complied with its Tameside duty. The court should intervene only if no reasonable authority could have considered its inquiries sufficient. The Planning Committee had enough information to decide the application, despite not having the precise parking-loss figure expressly stated at the meeting.
5. Evidence generated after the decision may be admitted where it elucidates, rather than fundamentally alters, the contemporaneous decision-making and does not contradict it. Mr Millard’s evidence was admissible but of limited weight because it explained Kent County Council’s consultation response and did not determine the issue.
6. Section 278 of the Highways Act 1980 did not provide a sufficient backstop for the Council’s decision. It had not featured in the relevant decision-making as a mechanism to prevent implementation pending park-and-ride expansion. The claim nevertheless failed on the substantive grounds.

First-instance judicial review. Permission to proceed on ground 2 was granted at a renewed oral application before Robert Palmer KC, sitting as a Deputy Judge of the High Court, on 18 September 2025. The claim was dismissed by the High Court (Planning Court).