Bristol Zoo Gardens - High Court prioritises open‑space quality; guidance on outdated technical standards

The High Court has dismissed a judicial review challenge to Bristol City Council’s (the “Defendant”) decision to grant planning permission for the redevelopment of the former Bristol Zoological Gardens site. The case, Save Bristol Gardens Alliance Ltd v Bristol City Council & Bristol Zoological Society [2025] EWHC 3191 (Admin) (“Save Bristol Gardens Alliance Ltd”), provides important guidance on how local planning authorities should approach evolving technical standards and policy requirements during the planning process.

Background

In June 2024, the Defendant granted permission for a major redevelopment of the historic zoological gardens site subject to conditions.

Save Bristol Gardens Alliance Ltd (the “Claimant”) challenged the permission on three grounds:

1. Biodiversity Net Gain (“BNG”): The Defendant acted unlawfully by accepting an assessment of the development’s contribution to BNG based on Natural England’s Biodiversity Metric 3.0 (“Metric 3.0”) rather than later versions (3.1 or 4.0).
2. Carbon emissions:  The Defendant relied on outdated criteria to measure the development’s projected carbon dioxide emissions by relying on L2013 instead of updated standards introduced in L2021.
3. Open space: The Defendant failed to assess whether the development would lead to a quantitative loss of open space and therefore was not able to properly apply national planning policy in accordance with the approach stated in R (Brommell) v Reading Borough Council [2018] EWHC 3529 (Admin)(“Brommell”)

Ground 1: BNG

The BNG report commissioned by the Defendant relied on Metric 3.0 to calculate the impact of development and the net change that could be achieved despite Metric 3.1 having been published. Guidance from Natural England (“NE”) advised that changing metrics mid-project could lead to discrepancies between calculations. The use of Metric 3.1 and the subsequently published Metric 4.0 was considered by the environmental consultants to be unreasonable and disproportionate. The Planning Officer’s Report, which the Planning Committee relied on, concurred with this assessment.

The Claimant acknowledged that the choice of metric is a discretionary decision but argued that accepting the use of Metric 3.0 was based on a misunderstanding of NE’s guidance and serious logical and methodological errors amounting to irrationality in the decision-making process. 

In dismissing this ground, the Court reasoned that the Claimant had failed to recognise the practicalities of preparing a large-scale project for a planning application and that it was reasonably open to the planning officer to proceed as it did, supported by the advice from NE.  It was however, observed in the judgment that had the objections raised by consultee Bristol Tree Forum in respect of the BNG assessment been irrefutable or accepted as correct by the Defendant’s Nature Conservation Officer or the Planning Officer, the Court may have had to probe deeper into the rationality of the decision to accept the metric. 

Ground 2: Carbon emissions

The proposed development was required to reduce carbon dioxide emissions from residual energy use by at least 20%, in accordance with BCS14 of the Bristol Core Strategy. The Defendant’s Climate Change and Sustainability Practice Note (CCSPN) advised developers to use the methodology in Part L of the Building Regulations. At the time the application was submitted, the applicable standard was L2013, but L2021 came into force two days after the application was validated. The Planning Officer considered it was common for technical guidance to change during such large-scale applications and that requiring a fresh assessment using L2021 would be disproportionate. 

The Claimant argued that the Defendant had failed to consider a material objection to the scheme demonstrating that in accordance with the updated methodology L2021. the development would only achieve a 14% reduction in emissions. 

The Court found that the application was prepared in accordance with guidance in force at submission and that Defendant’s January 2023 Addendum to the CCSPN expressly allowed schemes already in planning to retain the Part L 2013 methodology throughout the process. The planning officer’s conclusion that requiring a fresh assessment would be disproportionate was consistent with that policy. Further, the Defendant was not obliged to consider the estimations in respect of emissions under Part L 2021 since there were not “so obviously material” as to require the Planning Committee’s direct consideration. 

Ground 3: Open Space

The proposed development site was designated as ‘Important Open Space’ under local policy.  The key issue was whether the Defendant lawfully applied paragraph 99(b) of the National Planning Policy Framework (“NPPF”) which requires that any loss of open space be replaced by “equivalent or better provision in terms of quantity and quality. The Planning Officer considered that in light of the site’s unusual nature and the significant benefits to be derived from the development, the development would deliver a “marked qualitative enhancement” in open space provision. On quantity, the officer’s report recorded that it was difficult to conclude that the scheme would increase or even maintain the amount of open space.

The Claimant argued that the Defendant failed to advise whether the development would lead to a quantitative loss of open space, leaving the Planning Committee unable to apply the policy correctly in line with the Brommell approach, which requires judgment on both quantity and quality.

The Court held that the Defendant was not required to make precise findings on the amount of open space lost and replaced. It was sufficient for the planning officer to weigh both factors together. Their judgment that qualitative improvements outweighed any marginal quantitative deficit was reasonable and consistent with Brommell. Therefore paragraph 99(b) had been properly applied. 

Conclusion

This decision emphasises that local planning authorities are entitled to rely on technical standards and methodologies that are current when an application is prepared, and they are not required to apply updated standards retrospectively where practicalities and published policy support continue. Further, when applying paragraph 99(b) of the NPPF, authorities may lawfully balance qualitative improvements against any marginal quantitative loss of open space, if judgement is reasoned and proportionate.