In R (Manby) v Hackney [2026] EWHC 1543 (Admin), the High Court quashed a householder permission for a rear extension because of the way the council dealt with its Residential Extensions and Alterations SPD.

 

The 45-degree rule

The SPD said rear extensions should not exceed a line taken at 45 degrees from the centre of the nearest ground floor habitable room window in an adjoining property. In practical terms, it is a tool for assessing daylight, overshadowing, outlook, dominance and residential amenity.

The officer’s report referred to the rule and noted that it was relevant. But it did not go on to ask whether the rule was complied with, whether any infringement mattered, or whether permission should still be granted as a matter of planning judgment.

 

Just one tool in the box….

Counsel for the defendant described the 45-degree rule as just “one tool in the box” when assessing residential amenity. HHJ Russen KC’s response was memorable:

“…the tool has to be taken out of the box for the purposes of testing its usefulness.”

That is the line that should make anyone preparing, reviewing or relying on planning reports pause.

 

Delegated decisions and officer reports

Paragraph 70 is also worth noting. The court rejected the suggestion that the report was simply one officer writing for another decision-maker who could be assumed to bring local knowledge and common sense to bear “off the page”. Although signed on different dates, the report was signed by both officers and the reasons in it were treated as their reasons.

In short, in a delegated decision, the written report may be the decision-maker’s reasoning, not just background briefing material.

 

Why it matters

Supplementary guidance does not dictate the outcome in the same way as adopted policy, and it will often require planning judgment. But once guidance is materially engaged, especially where it has been raised in a detailed objection, the decision-maker has to do more than simply name-check it.

“Have regard to” means more than paying lip service.

 

Practical takeaways

• For planning officers: if a specific development management tool is engaged, apply it and explain the planning judgment.
• For consultants and developers: deal expressly with relevant supplementary guidance in the application material, especially where a departure may need to be justified.
• For objectors: a focused objection that identifies the relevant policy or guidance and links it to the site-specific impact can be much harder to ignore.
• Guidance may be flexible, but flexibility still requires analysis. A small householder case, but a much wider development management message.

 

For legal guidance and advice on how this judgement may apply to your business, please contact Maria O’Loan or another member of our Planning and Environment team.

While great care has been taken in the preparation of the content of this article, it does not purport to be a comprehensive statement of the relevant law and full professional advice should be taken before any action is taken in reliance on any item covered.