Parties Cannot Be Expected To Second-Guess Their Experts | Planning Inquiry Costs Award Quashed

A costs award against a council whose expert conceded key points under cross-examination has been quashed. There is no “normal procedural requirement” to test expert evidence, and parties cannot be expected to second-guess their experts.

HALTON BOROUGH COUNCIL V SECRETARY OF STATE FOR HOUSING, COMMUNITIES AND LOCAL GOVERNMENT [2025] EWCA Civ 1566

In The King (on the application of Halton Borough Council) v Secretary of State for Housing, Communities and Local Government [2025] EWCA Civ 1566, the Court of Appeal allowed the Council’s appeal against a partial costs award made following a called-in planning inquiry. After the Council’s expert witness conceded under cross-examination that he would advise refusing permission, the Council withdrew its support and the inquiry collapsed. The Secretary of State’s decision-maker found the withdrawal unreasonable under the Planning Practice Guidance and awarded costs to the HSE and Viridor Energy Limited under section 250(4) of the Local Government Act 1972. The Court of Appeal held the decision was legally flawed, identifying a critical contradiction in reasoning and ruling that expecting a party to ensure its expert evidence would withstand cross-examination was not a “normal procedural requirement“. A party is not expected to second-guess its expert. The Council’s withdrawal was for good reason and the costs orders were quashed.

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?

Citations

R v The Secretary of State for the Environment ex p North Norfolk DC [1994] 2 PLR 78 Considered that local planning authorities must produce evidence with some substance to support their stance, although it need not be sufficient to persuade the inspector; failure alone does not necessarily equate to unreasonableness. R v Secretary of State for the Environment ex p Wakefield MBC (1998) 75 P & CR 78 Held that there is an evidential threshold determining whether a planning authority’s conduct is unreasonable; even evidence meeting that threshold may not prevent a costs award if the authority persists despite overwhelming contrary evidence. R (Finch) v Surrey CC [2024] UKSC 20, [2024] PTSR 988 Confirmed that judicial review of discretionary decisions like costs awards applies a standard of irrationality, including reliance on irrelevant factors or logical/methodological errors in reasoning. R (KP) v Secretary of State for Foreign Commonwealth and Development Affairs [2025] EWHC 370 (Admin) Distinguished between process and outcome rationality, stating that process reasoning must avoid errors or evidential gaps that undermine the logic of the resulting decision. South Bucks DC v Porter [2004] UKHL 33, [2004] 1 WLR 1953 Stated that decision reasons must be intelligible and adequate, addressing principal issues and disclosing resolution of law or fact, but need not reference every material consideration. Guntrip v Cheney Coaches Ltd [2012] EWCA Civ 392 Noted that an expert witness has a legal duty to inform the tribunal if they can no longer support the case of the party that instructed them. R v Cornish [2016] EWHC 779 (QB) Held that although an expert’s evidence was undermined in cross-examination, the Crown’s reliance on it was not improper as the issues only became apparent during trial. R (DPP) v Aylesbury Crown Court [2017] EWHC 2987 (Admin), [2018] 4 WLR 30 Found that the CPS was not responsible for an expert’s error that led to case collapse, as the expert is an independent party and there was no obvious reason to doubt their conclusions beforehand.

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Key Points

A party’s reliance on its expert evidence is not unreasonable merely because it is later undermined in cross-examination. For such reliance to be unreasonable, there typically needs to be a trigger, such as an obvious flaw in the evidence or a clear challenge from the opposing side that should have caused the party to doubt its expert’s views.
There is no normal procedural requirement for a party to test or guarantee that its expert’s evidence will withstand cross-examination. An instructing party is entitled to rely on the independent expert it has engaged, and the subsequent failure of that evidence under scrutiny does not, without more, constitute unreasonable conduct.
Withdrawing support for a case following a material change in an expert witness’s evidence during proceedings is for good reason and is not, of itself, unreasonable behaviour justifying a costs award.
A finding of unreasonable conduct based on a failure to comply with procedural requirements must identify the specific requirement that was breached. A general assertion that a party should have better prepared its case is insufficient if it does not correspond to a recognised rule, direction, or established normal procedural requirement.
A costs decision based on contradictory reasoning—such as accepting a party acted due to new evidence while finding there was no material change in evidence—contains a demonstrable logical flaw and is liable to be quashed for irrationality.

"In my judgment this sets the bar too high. 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."

Key Findings In The Case

The Council withdrew support for the planning application after its expert witness, Mr Hopwood, significantly departed from his prior position under cross-examination, conceding that he would recommend refusal if acting as Inspector. This formed the immediate basis for the Council’s change in stance and was not previously anticipated [10–12, 34].
The Secretary of State’s costs decision accepted that the Council’s conduct in resolving to grant planning permission was not in itself unreasonable, and that the public safety objections from the HSE had been known and considered at that stage [15, 42–43].
The Council held multiple conferences involving senior counsel and its experts before and after submitting its evidence and had extensively discussed and appraised its case throughout the process, including after the HSE’s Rule 6 statement was served [8, 65].
The Secretary of State’s costs award was based on the finding that the Council’s reliance on Mr Hopwood’s expert evidence was unreasonable because they failed to ensure in advance that his evidence would withstand cross-examination; but the Court of Appeal found this reasoning flawed, as there was no procedural requirement to test expert evidence for resilience under cross-examination, nor was it shown that the expert’s views were untenable prior to giving oral evidence [17–20, 55–61].
The purported justification for the partial award of costs—that the Council withdrew its support “without good reason”—was found to be irrational, as the withdrawal followed a material change in expert evidence. The decision failed to identify any prior point at which the Council was or should have been aware that its position had become untenable, thus undermining the basis for a finding of unreasonable conduct [34–35, 39–40, 62].

"If Mr Parsons regarded the Council's withdrawal of support for the proposed development following the change in Mr Hopwood's evidence as being 'without good reason' I consider that his conclusion in that regard is untenable. If he meant to suggest that it is a 'normal procedural requirement' to go beyond the Council's extensive discussion of the parties' positions before Mr Hopwood's cross-examination, I can see no rational basis for that conclusion. If, on the other hand, he meant to identify some other 'normal procedural requirement' with which the Council did not comply, I do not understand what it was."

The Court of Appeal’s decision in R (Halton Borough Council) v Secretary of State for Housing, Communities and Local Government [2025] EWCA Civ 1566 establishes that parties to planning inquiries are not expected to second-guess their experts, and an expert’s concessions under cross-examination do not automatically justify a costs award.

Background

In September 2017, a developer, MJ Gleeson, submitted a planning application to Halton Borough Council for 139 dwellings on land in Runcorn. The Health and Safety Executive objected on public safety grounds due to the site’s proximity to the Runcorn Chemicals Complex. Despite this, the Council resolved to grant permission, relying on its adopted development plan and advice from its specialist risk consultants, DNV.

Consequently, the Secretary of State called in the application in May 2021. A public inquiry was scheduled. The Council and HSE served statements of case and proofs of evidence. The Council’s evidence on public safety was given by its expert, Mr Hopwood of DNV. The developer submitted a position statement indicating that, as the public safety matter was between the Council and the HSE, it would rely on the Council to provide evidence in support of the application [§6]. A national security direction was made, meaning part of the inquiry would be held in private.

The inquiry opened on 11 January 2022. In closed session on 13 January, Mr Hopwood was cross-examined by Mr Kimblin QC on behalf of the HSE [§10]. Under questioning, he conceded that the local policy relied upon by the Council failed to follow the principles in the National Planning Policy Guidance and that, following those principles, he would advise strongly against granting permission. This was inconsistent with his previous advice.

Faced with this, the Council withdrew its support for the development. The applicant then withdrew the planning application, causing the inquiry to collapse. Both the HSE and another interested party, Viridor Energy Limited (which operated one of the UK’s largest energy-from-waste plants near the site [§7]), applied for their costs of participating in the aborted inquiry against the Council.

On 27 July 2022, the Secretary of State’s decision-maker, Mr Parsons, allowed the applications in part. He found the Council’s decision to withdraw its support when it did was unreasonable, causing the other parties to incur unnecessary wasted expense. He awarded costs from the date of their Rule 6 statements. The Council’s application for judicial review of this costs decision was dismissed by Fordham J. The Council appealed to the Court of Appeal.

Costs Issues Before the Court

The central issue on appeal was whether the Secretary of State’s decision to award costs against the Council was lawful. This required examination of whether the finding of unreasonable conduct was rational and whether adequate reasons were given. The case turned on the application of the Secretary of State’s Planning Practice Guidance on awards of costs, particularly in the context of a called-in application. The court had to consider whether the Council’s reliance on its expert’s evidence up to the point of his damaging cross-examination, and its subsequent withdrawal of support, constituted a failure to comply with “normal procedural requirements” or was otherwise unreasonable behaviour justifying a costs award.

The Parties’ Positions

The Council argued that Mr Parsons’ decision was flawed. It contended that its withdrawal of support was a direct and reasonable consequence of its expert witness changing his evidence under cross-examination, which was a material change in circumstances. It submitted that there was no identifiable “normal procedural requirement” it had breached and that it was not unreasonable to rely on its appointed expert’s written evidence until it was tested and found wanting during the inquiry. The Council drew an analogy with criminal costs cases, arguing that a party is not responsible for an expert’s unexpected failure under cross-examination unless the evidence was obviously untenable from the outset [§46-51].

The Secretary of State defended the decision. It was argued that the Council had a responsibility to ensure its evidence was robust enough to withstand scrutiny and to continuously appraise its position as the inquiry progressed. The submission was that the Council’s late withdrawal, after the other parties had incurred substantial preparation costs, was a procedural failure that amounted to unreasonable behaviour. The Secretary of State maintained that the reasons given were adequate and the decision was within the bounds of rationality.

The Court’s Decision

The Court of Appeal unanimously allowed the appeal. Lord Justice Lewison, giving the lead judgment (with which Lady Justice Asplin and Lord Justice Coulson agreed [§69-70]), identified demonstrable flaws in the reasoning of the costs decision.

First, the court found an irreconcilable contradiction in Mr Parsons’ reasoning. He accepted the Council withdrew support due to new evidence given under cross-examination, yet simultaneously concluded there had been “no material change in the evidence” [§35]. This was a clear logical error — “a leap in reasoning which fails to justify the conclusion” and “a demonstrable flaw in the reasoning” [§35].

Second, the court held that the decision-maker set the bar too high in effectively requiring a party to guarantee its expert evidence would survive cross-examination [§59]. The judgment clarified that testing an expert’s evidence to see if it would withstand cross-examination is not a “normal procedural requirement” in planning inquiries [§61]. The reason for instructing an expert is their independent expertise, which the instructing party does not possess. A party is not expected to second-guess its expert as a matter of routine [§61]. The mere fact that an expert’s evidence is later undermined does not, without more, render the party’s prior reliance on it unreasonable [§45].

The court noted the Council had held multiple conferences with its expert and counsel, which aligned with good practice recommended by the RTPI [§65]. There was no finding that the expert’s initial proof was obviously flawed or failed to provide a “respectable basis” for the Council’s position [§57]. Furthermore, the damaging concessions related to the validity of local policy — a matter not obviously within the public safety expert’s core remit — making it harder to foresee that such questions would be put to him [§66].

The judgment emphasised that the costs decision failed to identify what the Council did wrong or at what point its conduct became unreasonable [§62]. There was no specific procedural rule breached, nor any direction from the inspector ignored [§55]. The link between the withdrawal and a finding of unreasonable conduct was, therefore, “tenuous, to say the least” [§62]. The Court of Appeal concluded that the Council had a good reason to withdraw when it did and that the finding of unreasonable behaviour was untenable [§67].

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