Thornhill Estates Ltd v Secretary of State for Housing, Communities And Local Government

In a statutory planning review, the classification of a measure as a planning benefit or as mitigation is not a rigid legal question. Mitigation may produce incremental or net benefits, but the decision-maker may assess those matters in context and attach little or no weight to them. The weight given to material considerations is a matter of planning judgment, subject only to the limits of rationality. A decision letter must be read fairly, as a whole and in a straightforward manner. The court must not substitute its own planning assessment for that of the decision-maker. A failure to describe mitigation as a benefit is not, without more, irrational.

The claimant sought statutory review under section 288 of the Town and Country Planning Act 1990 of the Secretary of State’s decision dated 22 February 2018. The decision dismissed an appeal against the deemed refusal of outline planning permission for 300 dwellings and associated works in Leeds.

The inspector had recommended allowing the appeal. The Secretary of State disagreed with the inspector’s treatment of highway capacity and safety works and the reservation of a possible primary-school site. He regarded those matters as mitigation rather than planning benefits, although he accepted other benefits and conducted the relevant planning balances. The issue was whether that approach was irrational.

1. The claim was dismissed. The Secretary of State was entitled to reach a different planning balance from the inspector. The challenge was not concerned with the amount of weight given to the various considerations, but with the contention that the three disputed matters had been excluded from the planning balance by an irrational characterisation.
2. Planning benefits and mitigation are not fixed terms of art or mutually exclusive legal categories. Mitigation may generate incremental or net benefits, but the decision-maker may regard those benefits as arising from measures required to accommodate the development’s adverse effects and may give them little or no significant weight. That conclusion depends on the context, the nature of the planning exercise and the decision letter as a whole.
3. The Secretary of State had recognised the factual effects of the highway works and the school-site reservation. His conclusion was that their significance arose from the need to mitigate impacts created by the development. That was a permissible exercise of planning judgment and was not internally inconsistent with giving weight to the cycleway, which was treated as a freestanding benefit rather than mitigation.
4. The statements of common ground did not have to be read as statutes or followed slavishly. Their references to mitigation and benefit had to be understood in context. The Secretary of State was entitled to identify the substantive distinction he considered relevant and to disagree with the inspector on the weight to be given to the disputed matters.
5. Under section 38(6) of the Planning and Compulsory Purchase Act 2004, the development plan retained priority, while the NPPF operated as a material consideration. The various planning balances, including those under paragraph 14 of the NPPF and the heritage balance under paragraph 134, culminated in the statutory planning judgment. The court’s role was supervisory, not a review of planning merits.
6. The decision letter was detailed, carefully structured and logically intelligible. It made clear both the disagreement with the inspector and the reason for it. The alleged error of reasoning was therefore not established.

The judgment describes an earlier Secretary of State decision being quashed by the High Court on 4 November 2015. A reopened inquiry was held in January 2017. The present claim was a first-instance statutory review of the Secretary of State’s subsequent decision.