Background
Bronwen Manby, the claimant and owner of 89 Culford Road in Hackney, challenged the London Borough of Hackney’s decision to grant planning permission for residential extensions at the neighboring property, 87 Culford Road. The proposed development included a single-storey lower ground floor extension (extending 2 meters beyond the existing extension), an upper ground floor rear extension of 1.5 meters, and a mansard roof extension.
The Hackney Residential Extensions and Alterations Supplementary Planning Document (SPD, April 2009) contains specific design guidance requiring all extensions to comply with the “45-degree rule” to prevent overshadowing and loss of amenity for neighbors. This rule operates as a guide: an extension should not exceed a line taken at 45 degrees from the center of the nearest ground floor window of a habitable room in an adjoining property. The rule is assessed on both plan and elevation.
Manby objected that the proposed extension breached the 45-degree rule regarding her property, particularly citing loss of daylight, sunlight, and visual amenity to her kitchen and garden. The planning officer’s report (OR) recommended approval without explicitly determining whether the 45-degree rule was complied with in relation to No. 89, though it noted the 45-degree rule as a guide and concluded the extension would not result in unacceptable detrimental impact to neighboring amenity.
The Court’s Holding
HHJ Russen KC examined whether the planning authority was under a legal obligation to determine whether the 45-degree rule was met regarding the claimant’s property, and whether failure to do so constituted an error of law. The judge considered three alternative formulations of the claimant’s principal ground: (1) if the officer determined compliance, whether this involved a mistake of fact; (2) if the officer proceeded without determining compliance, whether this was a failure to consider a material consideration; or (3) if the officer determined non-compliance but approved anyway, whether adequate reasons were given.
The court analyzed when a planning authority becomes obliged to consider the 45-degree rule despite its status as guidance rather than binding policy. Under section 70(2) of the Town and Country Planning Act 1990, local planning authorities must have regard to “material considerations.” While the SPD itself is not part of the adopted development plan (unlike Policy LP17 which directs regard to the SPD), the SPD is a material consideration. The court adopted the test from R (ClientEarth) v Secretary of State for Business, Energy and Industrial Strategy [2020] EWHC 1303 (Admin): a decision-maker fails to take a material consideration into account only when they were under an express or implied obligation to do so, or when the matter was so “obviously material” that failure to consider it would be irrational.
Evidence from the planning officer, Ms. Hadadi, clarified her approach: she considered the 45-degree rule as “a guide to be applied flexibly,” did not determine whether strict compliance was achieved, did not perform calculations or draw diagrams to verify compliance regarding No. 89, and later stated she did not recall whether she believed the rule was met when drafting the report. However, she maintained that the overall acceptability of the proposal was demonstrated through other means and that any breach would be “minor” given the extension’s characteristics. The court examined whether this constituted process irrationality (a flaw in reasoning leading to the decision) or a breach of the Tameside duty (the obligation to take reasonable steps to inform oneself of relevant information before deciding).
Key Takeaways
- Supplementary Planning Documents are material considerations but do not carry the weight of adopted development plan policy; their application requires exercise of planning judgment.
- A decision-maker’s failure to address a material consideration is actionable only when they were under a legal obligation to do so (express, implied, or through irrationality of not considering it when obviously material).
- Planning officers’ reports need not address every applicable policy detail in equal depth, particularly in delegated decisions; courts apply caution before finding error in process rationality.
- Guidance documents framed as requiring “regard” or permitting application “as a guide” may allow flexibility that does not mandate formal compliance determination in every circumstance.
- The Tameside duty requires only reasonable steps to inform oneself; a decision-maker need not conduct exhaustive investigations unless no reasonable authority could suppose their inquiries were sufficient.
Why It Matters
This judgment clarifies the extent to which planning authorities must engage with design guidance in supplementary planning documents when making neighbor-affecting decisions. Development affecting residential amenity commonly invokes SPD guidance, yet officers face volume pressures. The court’s framework—distinguishing between material considerations and binding policy, and between flexibility in guidance and irrationality in disregarding it—establishes that officers need not produce formal compliance calculations for every applicable rule provided their overall reasoning is sound and not logically flawed.
For neighbors challenging permissions, the decision sets a higher bar for proving error: objectors must show the authority was obliged to determine a particular issue, not merely that the officer should have given it more attention. The judgment also reinforces that process irrationality requires a demonstrable logical flaw or gap in reasoning—mere omission of discussion does not suffice if the outcome itself was rational. This has practical implications for residential extension disputes, where the 45-degree rule and similar SPD guidance are frequently contested.