DEE & DEE v SECRETARY OF STATE FOR LEVELLING UP HOUSING AND COMMUNITIES & Anor

An inspector’s decision may be quashed for a material mistake of fact where the mistake forms part of the planning judgment and the court cannot be satisfied that the outcome would necessarily have been the same without it. The test is not confined to cases in which the error affects a numerical calculation. A decision letter must be read as a whole. References to the likely effects of permitted development on a dwelling’s appearance, scale, mass, local character and housing stock may show that the mistaken understanding was significant to the reasoning. Where the error is substantial or significant and the counterfactual outcome is not necessarily identical, remission for reconsideration is appropriate.

The claimants brought a statutory challenge to an inspector’s dismissal of their appeal under section 78 of the Town and Country Planning Act 1990. The appeal concerned conditions attached to planning permission for alterations and extensions to a dwelling wholly within the New Forest National Park. The conditions restricted specified permitted development rights under the Town and Country Planning (General Permitted Development) (England) Order 2015.

It was accepted that the inspector had misunderstood the permitted development rights applying inside and outside a National Park. The central issue was whether that mistake was material and required the decision to be quashed and remitted.

Claim allowed; decision quashed and remitted.

1. The applicable approach was that stated in Simplex GE (Holdings) Limited & Another v Secretary of State for the Environment & Another [2017] PTSR 1041. To avoid quashing, it had to be shown that the decision would necessarily have been the same despite the mistake. The error had to be substantial or significant, rather than insubstantial or insignificant.
2. The inspector’s decision letter was succinct and had to be read as a whole. The inspector did not merely apply the 30% floor-space limit in policy DP36. He assessed the permitted development rights removed and considered that further works might include large side and rear additions altering the dwelling’s appearance and significantly increasing its scale and mass.
3. That reasoning was material because it engaged the wider aims of policy DP36, including protection of local distinctive character and maintenance of a balanced range and mix of housing. The inspector had made a clear mistake about the rights available within the National Park, including side extensions and potentially rear extensions.
4. The site visit and the references to appearance, scale, mass and incremental unsympathetic extension reinforced that the decision involved planning judgment, not a purely arithmetical assessment of whether the 30% limit would be exceeded. The court was not satisfied that the decision would necessarily have been the same without the mistake.
5. The mistake was therefore substantial or significant and material to the decision. The inspector’s decision was quashed and remitted to the Secretary of State for reconsideration.

First-instance statutory challenge. The judgment does not state any earlier judicial decision in the same proceedings.