Christmas Caselaw: BNG in the High Court and Costs in the Court of Appeal

Whilst we wait for the next festive consultation to drop,* this blog takes a brief sojourn in the relative calm of the Administrative Courts.

There are two cases that we are going to look this week. The first is a High Court case that looks at the application of non-statutory BNG. The second is a Court of Appeal decision about costs awards at planning inquiries.

Save Bristol Gardens Alliance Ltd v Bristol City Council [2025] EWHC 3191 (Admin)

Save Bristol Gardens is a decision about the redevelopment of Bristol Zoo. Not the new site, but the one I went to as a child, with the Monkey Temple (which is now listed) and the elephants that my mum swore used to be on tv.

Anyway, on 28 June 2024, Bristol City Council granted planning permission to redevelop the site for “196 residential units (Class C3), the provision of community floorspace (Class E, F1 and F2), and open space with associated landscaping, play space, parking, accesses (pedestrian, cycle and vehicular), infrastructure, works to listed buildings and selective demolition of buildings.”

The application was submitted before the statutory BNG regime came into force – which is crucial to understanding the rest of the case – so please do keep that in mind.

The permission was challenged on three grounds:

1. The Council acted unlawfully in adopting the planning officer’s advice and recommendation that the development’s contribution to biodiversity net gain should be measured by applying Natural England’s “Biodiversity Metric 3.0” published on 7 July 2021 – as opposed to the later version introduced by the time the application was determined.
2. The Council acted unlawfully in adopting out of date criteria to measure the development’s projected carbon dioxide emissions.
3. The planning officer failed to advise whether the development would lead to a quantitative loss of open space, with the result that the Defendant was not in a position properly to apply national planning policy.

The claim failed on all three grounds.

On Ground 1, the Court found that there had been no legal error or irrationality in the planning officer’s reasoning about the ability of the site to deliver BNG, or the suitability of the assessments that had been conducted. This was, in part, because of “the practicalities of preparing a project or scheme with a view to submitting an application for planning permission….. the process of assessment using the biodiversity metric is iterative and should be seen as integral to project design from the earliest possible stage. In the case of development of land such as the site, which has significant biodiversity value in its existing state, ecological survey of the site, and early consideration of the results of that survey, are likely to be an important driver of the early stages of project design.“

Ground 2 failed because the standards used to measure the development’s projected emissions were those in effect when the application was prepared, and the Council’s adopted policy position was that those standards should continue to be used throughout the determination process. This was held to be entirely lawful.

On Ground 3, the Court held that “It was not a necessary prerequisite to a proper application of paragraph 99(b) of the Framework that the planning officer make precise findings as to the amount of existing open space lost to the development and the amount of open space provided by way of replacement. It was sufficient for the planning officer to follow what was, in substance, a precautionary approach.”

Now, the outcome on Ground 1 may well have been different if the application had been subject to the statutory BNG regime… but nonetheless it is a useful reminder of the importance of designing BNG into a scheme at the earliest possible moment, and that the Courts may well side with you if you do take the iterative approach to assessment seriously.

Halton Borough Council, R (On the Application Of) v Secretary of State for Housing, Communities and Local Government [2025] EWCA Civ 1566

Halton Borough Council is about as different a set of circumstances as it is possible to get.

In this case, the Court of Appeal was asked to decide whether it was reasonable to make a costs award against a Council, when the evidence given by the Council’s instructed expert witness unexpectedly causes the inquiry to collapse.

The facts of the case are interesting, and well worth reading in full, but I am not going to repeat them here, as it is getting late and I might still be wearing reindeer antlers**.

The Court of Appeal decided that the costs award, in this instance, was a step to far, finding that:

“59. … In any case in which there is a difference of expert opinion, the decision-maker is likely to resolve the difference in favour of one expert rather than another, especially where the experts have been cross-examined. In that sense the expert evidence called on behalf of the losing party will not have stood up to scrutiny following cross-examination. But that of itself cannot rationally be regarded as unreasonable behaviour.

60. As I have said, Mr Parsons did not suggest that the Council had initially fallen below the required evidential threshold. But he went on to say that the Council should have satisfied themselves that Mr Hopwood’s evidence would stand up to “scrutiny by any other parties through cross-examination”. That seems to me to be the nub of his reasoning. The question, then, is what must a party do, having instructed an apparently competent expert, to test the reliability of their expert evidence? And if they fail to do so, is that unreasonable conduct by that party?

61. There is no suggestion in the cases that we have seen that the LPA (or, indeed any other party) should, as a generality, test the evidence of its own expert to see if it would withstand cross-examination. In other words, testing the evidence of an expert to see whether it would stand up to cross-examination cannot be described as a “normal procedural requirement” even if it is permissible procedural option. Nor am I aware of any procedural requirement to that effect in civil proceedings. As Sharp LJ said in Aylesbury, the reason why a party instructs an expert is that the expert has expertise that the party instructing them does not have. Why, then, should the instructing party be expected to second guess the expert as a matter of routine? The position may be different where the party calling the expert knew, or should have known in the light of subsequent events, that the expert’s views were untenable; or where there is some obvious flaw in the expert’s reasoning. But Mr Parsons did not identify any time or event which would have led the Council to that conclusion.

62. In short, the Council cannot tell from Mr Parsons’ decisions what it did wrong or when its case changed from being “respectable” to “unreasonable”. When Mr Williams was asked to identify when and why the change took place, he was unable to do so. Moreover, if it was unreasonable conduct on the part of the Council to continue to rely on Mr Hopwood’s expert evidence, it would not have mattered whether the Council withdrew its support for the development or soldiered on to the bitter end. So the link between the withdrawal of the Council’s support and the finding of unreasonable conduct is tenuous, to say the least.”

Historic England Lists a Shipwreck

And finally, this week Historic England published its annual list of remarkable places listed over the last twelve months.

Amongst the new listed buildings and scheduled monuments deemed worthy of protection in 2025 are:

• A series of “Dragons Teeth” anti-tank defences in Thorneycroft Wood, Guildford
• A shipwreck off the Dorset coast; and
• A set of mews studios in Camden, which are far too young to have been listed, having been constructed between 1987 and 1989.

Which means that all of Gen X and a not-insignificant number of elder-millennials have just joined the ranks of those people who are officially older than a a listed building….

Merry Christmas!

*with recent rumours indicating that the latest NPPF consultation, draft NDMPs and the outcome of the BNG small sites consultation may all arrive in the next week or two…

** an occupational hazard when you write a blog immediately upon getting home after the office Christmas Party.