Watt, R (on the application of) v London Borough of Hackney & Anor

A planning decision may be quashed for a material mistake of fact where the mistake creates an objectively unfair decision-making process. The relevant fact must be established and objectively verifiable, the claimant must not be responsible for the mistake, and the mistake must have played a material, though not necessarily decisive, part in the reasoning. The court reviews legality, not the planning merits. A corrected assessment which remains above a recognised planning benchmark does not necessarily cure the error if the decision-maker relied on a materially misleading description of the evidence.

The claimant sought judicial review of Hackney’s resolution granting planning permission for a café and flats beside a listed primary school in a conservation area. The principal issue concerned the effect of the development on sunlight in the school’s external area.

The planning committee relied on a sunlight assessment which had modelled solid boundary walls as permeable fences and described compliance with BRE guidance as comfortable. Further expert evidence showed a materially greater reduction in sunlight. The court considered whether the error justified quashing the permission and rejected the claimant’s other grounds.

1. Claim allowed. The planning permission was quashed because the committee’s decision was materially affected by a mistake of fact concerning the modelling of the school’s boundary walls.
2. The court applied the principles stated in E v Home Secretary [2004] EWCA Civ 49. A mistake of fact giving rise to unfairness requires: a mistake about an existing fact or available evidence; an established fact that is objectively verifiable and uncontentious; no responsibility on the claimant’s part; and a material part played by the mistake in the decision-maker’s reasoning.
3. The modelling error was established and undisputed, although experts disagreed about its precise consequences. The claimant was not responsible for it. The officer treated the assessment as authoritative and advised the committee that the relevant benchmark was comfortably met. The misleading picture therefore disadvantaged objectors on a critical issue and materially influenced the decision.
4. The court applied the materiality approach in Simplex GE (Holdings) Ltd v Secretary of State for the Environment (1989) 57 P&CR 306. It was sufficient that the error may have affected the decision; it need not have been decisive. The corrected figures remained above the 50 per cent guideline, but the substantial reduction in sunlight and the loss of the description “comfortably met” meant that the court could not say the error had made no difference.
5. The remaining grounds failed. The labels “outdoor classroom” and “playground” did not determine the issue; the area’s value and use were what mattered. The statutory duties concerning listed buildings and conservation areas had been addressed, the development did not cause a loss of educational provision, the earlier refusal had been considered, and no adjournment or further consultation was required.
6. The court was neutral on the planning merits. Hackney was to reconsider the application. Costs were divided by reference to the date on which the successful mistake-of-fact ground was advanced, subject to the stated Aarhus cap and exclusions.