Expert Cross-Examination in Judicial Review Requires Necessity Linked to a Pleaded Ground

1. Introduction

This judgment clarifies when expert witnesses may be cross-examined in judicial review proceedings. Its central distinction is between demonstrating that experts disagree and demonstrating that resolving their disagreement through cross-examination is necessary to decide a pleaded issue.

The High Court refused Blue Ireland Coalition CLG’s application to cross-examine two witnesses who had provided affidavits for Codling Wind Park Limited (“CWP”). Although genuine differences of expert opinion existed, Blue Ireland had not adequately connected the proposed questioning to specific grounds of its challenge. The application was also premature in important respects and sought an excessively wide-ranging examination.

The ruling was interlocutory: it determined an evidential application, not the legality of the maritime licence under challenge. It did not decide the meaning of “disturbance” under Article 12 of the Habitats Directive, whether the licensed surveys breached that provision, or whether the disputed expert evidence was admissible.

2. Background and Environmental Context

CWP proposes to develop an offshore wind farm on the Codling bank, between approximately 13 and 22 kilometres off the Wicklow coast. Before finalising the project’s design, it sought permission to undertake surveys and investigations. The Maritime Area Regulatory Authority (“MARA”) granted maritime usage licence MUL230034 on 23 February 2026 for three years, covering approximately 477 square kilometres.

Blue Ireland challenged that licence and obtained leave to seek judicial review on 11 May 2026. The proceedings concern, among other matters, the protection of harbour porpoises from the effects of survey activities and underwater noise.

Cetaceans are listed in Annex IV(a) to the Habitats Directive. Article 12 requires a system of strict protection, including prohibitions on deliberate disturbance and on deterioration or destruction of breeding sites or resting places. The assessments also addressed the conservation objectives of the Rockabill to Dalkey Island Special Area of Conservation (“SAC”).

The expert evidence

The judgment records that MARA commissioned an ecological report which criticised the licence and supporting assessments. The ecologist’s report, dated 29 May 2026, was exhibited to an affidavit sworn on 5 June 2026 and relied upon by Blue Ireland. Both documents therefore postdated the licensing decision and the grant of leave.

A marine mammal consultant involved in preparing CWP’s application documentation disputed the ecologist’s analysis. Further affidavits followed on both sides. CWP’s offshore licensing manager also gave evidence, particularly concerning the assessment of simultaneous survey operations and Condition 29 of the licence.

Blue Ireland sought cross-examination by reference to a spreadsheet containing 328 rows and seven columns. Many entries did not identify an alleged conflict in the relevant column. Its counsel described the proposed questioning as a “wide-ranging cross-examination of all the points of disagreement”. That breadth became a significant reason for refusing the application.

3. Summary of the Decision

• Expert opinions can justify cross-examination: disagreement about primary facts is not a prerequisite. Disputes about methodology, interpretation of scientific data or expert inferences may qualify.
• Necessity must be demonstrated: the applicant must connect the conflict to a pleaded issue and explain why that issue cannot justly be decided without cross-examination.
• Legal interpretation remains for the court: disagreement over the legal meaning of “disturbance” was not an appropriate subject for expert cross-examination.
• The proposed examination was insufficiently focused: identifying numerous disagreements did not establish their materiality to the actual grounds of challenge.
• The application was contingent and premature: the scientific disputes principally supported fallback arguments, while admissibility and the permissible use of the evidence remained unresolved.

The motion was refused. However, the trial judge remained free to revisit cross-examination if disputed expert evidence later proved crucial to a pleaded issue requiring determination.

4. Precedents Cited and Their Influence

4.1 Fairness when challenging sworn evidence

In RAS Medical Limited v Royal College of Surgeons [2019] 1 IR 63, the Supreme Court addressed a material factual dispute about which guidelines had been used in an accreditation process. The passages reproduced from paragraphs 88, 92 and 93 establish that a party ordinarily cannot invite a court to reject sworn evidence as unreliable or lacking credibility without giving the witness an opportunity to answer the criticism through cross-examination.

The authority also places responsibility on the party bearing the burden of establishing a contested fact to use the appropriate procedure where resolving the conflict is necessary. Nevertheless, it distinguishes an attack on credibility or reliability from an argument that evidence, even accepted, is insufficient to prove what is required.

Conlon J did not treat this authority as making cross-examination automatic whenever affidavits differ. Its fairness requirements must operate alongside the separate requirements of materiality, necessity and the limited function of judicial review.

4.2 Factual witnesses and expert witnesses require different treatment

Ethical Farming Ireland v Minister for Agriculture & Ors [2026] IEHC 42 had identified the relevant passages from RAS Medical Limited v Royal College of Surgeons. However, Cahill J expressly excluded expert cross-examination from the scope of that ruling.

That limitation mattered here. A factual witness’s interpretation or submission is not equivalent to an expert’s professional interpretation of scientific evidence. Rules directed at witnesses of fact should not be applied so broadly that they prevent legitimate testing of expert opinion.

4.3 Cross-examination must be targeted, not exploratory

In Friends of the Irish Environment and others v Environmental Protection Agency [2026] IEHC 415, Farrell J explained that cross-examination in judicial review is directed towards resolving evidential conflicts necessary to determine material issues. It is not a means of filling gaps in a party’s evidence or conducting a roving inquiry.

That decision also recognised that expert opinion may be challenged through its underlying facts, methodology or interpretation of agreed facts. Conlon J rejected the suggestion that it prohibited questioning experts about inferences. He read its observations about interpretations and submissions in factual affidavits in their proper context, rather than as a general exclusion of expert cross-examination.

This authority therefore supported both sides of the present court’s approach: expert opinion can be tested, but the examination must remain confined to disputes whose resolution is necessary.

4.4 A genuine dispute of expert opinion may be sufficient

Salmon Watch Ireland CLG v Aquaculture Licences Appeals Board [2023] IEHC 129 supplied a particularly direct formulation. Holland J stated that cross-examination is necessary only where facts—or, for experts, opinions—are genuinely disputed and resolving the dispute is material to determining the proceedings.

This supported Conlon J’s express conclusion that an expert disagreement about primary facts is not a precondition. The relevant conflict may concern scientific opinion, including predictions drawn from accepted data.

4.5 The applicant must establish both conflict and necessity

In Hegarty v Commissioner of An Garda Siochana [2021] IECA 328, the Court of Appeal quoted the test stated in Irish Bank Resolution Corporation Ltd (in special liquidation) v Moran [2013] IEHC 295. An applicant must demonstrate:

1. The probable existence of a conflict on the affidavits relevant to an issue requiring determination; and
2. That the issue cannot justly be decided without cross-examination.

Although those cases did not concern expert evidence, their necessity requirement was central here. Since pleadings define the issues, showing relevance requires engagement with the statement of grounds. A catalogue of scientific disagreements cannot replace that exercise.

4.6 Post-decision evidence: identifying omissions, not retrying scientific merits

Hayes v EPA [2024] IECA 162 provided the principal framework for considering expert evidence that was not before the administrative decision-maker.

In the passages from paragraphs 130–133 reproduced by Conlon J, Butler J emphasised that the specialist regulator, rather than the reviewing court, resolves scientific conflicts within the statutory process. Judicial review does not permit a disappointed participant to introduce new scientific evidence simply to obtain a different assessment of the merits.

However, expert assistance may be needed to reveal an omission in an appropriate assessment which would not be apparent to a non-specialist court. An apparently complete administrative record may conceal a scientifically important issue that was never addressed.

The distinction is therefore between:

• Evidence identifying an important question that the assessment omitted; and
• Evidence inviting the court to prefer a new scientific answer to a question already assessed.

Conlon J accepted that expert evidence can expose an assessment gap and, for the sake of argument, accepted that this possibility could extend to an Article 12/Annex IV assessment. He did not decide the admissibility of the particular evidence before him.

4.7 Other environmental assessment authorities

The judgment also records reference to Case C-127/02 Waddenzee; Case C-258/11 Sweetman; Reid (No 1) v An Bord Pleanála [2021] IEHC 230; Environmental Trust Ireland v An Bord Pleanála [2022] IEHC 540; and Foran v An Coimisiún Pleanála [2026] IEHC 23.

These authorities formed part of the submissions concerning appropriate assessment and the use of expert evidence not presented to the decision-maker. The judgment did not separately analyse their holdings. It would therefore overstate their role to attribute a distinct new rule to each in this motion; the detailed reasoning relied principally on Hayes v EPA.

Case C-383/09. Commission v France appeared in the particulars of Ground 10, supporting Blue Ireland’s argument about breeding sites, resting places and habitat needed for the species’ life cycle. The court identified a potentially expert-sensitive omission under that ground but did not determine the pleaded proposition or its application.

4.8 Authorities appearing in the applicant’s alternative arguments

Blue Ireland invoked XJS, [1986] IR 750, for an ordinary, non-expert reading of planning documents. Its argument was that displacement caused by survey noise could be recognised as disturbance without resolving scientific disagreements.

It also referred to O'Donoghue and Carrownagowan, [2024] IEHC 300, paragraph 182, when arguing that evidence of environmental significance might be necessary to resist a “harmless error” argument at the remedial stage. The judgment provides no fuller citation for O'Donoghue.

These were submissions explaining why expert evidence might eventually matter. Conlon J did not decide those arguments or adopt a harmless-error conclusion. Their contingent character instead reinforced his concern that cross-examination was not presently shown to be necessary.

5. Analysis of the Court’s Reasoning

5.1 Identifying what kind of disagreement exists

The court distinguished disagreements about primary facts, legal terminology, selection of data, methods of analysis and inferences drawn from the data. Most disputes fell outside the first category.

For example, the experts did not fundamentally disagree about the existence of survey activities or the presence of calves and lactating females. They disagreed about the ecological consequences of those matters and the adequacy of the assessments.

Other disputes concerned:

• The disturbance footprint: whether the estimate that 31.1% of the SAC could potentially be affected represented a significant ecological concern, having regard to the developer’s explanation that it was precautionary and did not describe simultaneous daily effects.
• Population and habitat evidence: what conclusions could be drawn from survey data, and whether waters functionally connected to the SAC had been sufficiently considered.
• Mitigation: whether measures addressing injury also adequately addressed behavioural disturbance, displacement and residual effects.
• Foraging: the relevance of research concerning vessel noise to the consequences of the proposed survey activities.
• Cumulative effects: whether Condition 29’s separation requirements adequately addressed simultaneous operations and their combined disturbance footprint.

Those were potentially legitimate subjects of expert questioning. But their existence did not answer whether the court needed to resolve them to determine this particular challenge. The judgment’s descriptions of the scientific disputes were expressly provisional, not findings on their merits.

5.2 Scientific effects and legal “disturbance” are separate questions

The experts could potentially assist with the effects of noise, displacement, feeding disruption or exposure during breeding. They could not determine the legal meaning of Article 12.

That distinction was especially important because Blue Ireland’s principal case was that foreseeable displacement constituted prohibited disturbance without any additional threshold of environmental significance. Whether that legal interpretation was correct remained for the substantive hearing.

The judgment therefore does not establish either that all displacement breaches Article 12 or that only ecologically significant displacement does so.

5.3 The missing connection to the pleaded grounds

The decisive weakness was the failure to explain which pleaded grounds required which scientific disputes to be resolved. Blue Ireland’s submissions did not analyse the statement of grounds. When asked, counsel referred generally to Grounds 3–9 without addressing them individually.

CWP did address the grounds. The court’s resulting observations were provisional because they lacked developed argument from Blue Ireland:

Ground 10 illustrates the court’s restraint. A failure to identify breeding sites or assess their ecological functionality might require expert explanation. Nevertheless, the court would not construct the necessary argument itself when Blue Ireland had not advanced it and CWP had not had an opportunity to respond.

5.4 Admissibility, purpose and timing

At the parties’ request, admissibility was reserved to the trial judge. Conlon J nevertheless considered the proposed purpose of the evidence relevant to the cross-examination application.

Evidence admitted to explain an omitted assessment question is not necessarily available to establish that the regulator reached the wrong scientific conclusion. Its permissible use therefore affects which conflicts, if any, need resolution.

Furthermore, Blue Ireland’s scientific-significance arguments were alternatives to its principal legal case. If the legal arguments succeeded, the disputed significance questions might never arise. If those arguments failed, further questions about admissibility and relevance would remain.

Blue Ireland itself suggested that the hearing might be divided into stages, addressing the main legal argument first. The court did not order that arrangement, but the suggestion demonstrated why immediate cross-examination had not been justified.

5.5 Breadth cannot substitute for precision

The proposed examination effectively embraced every disagreement between the experts. That approach conflicted with the prohibition on roving cross-examination.

A large schedule may document the existence of disagreement, but it must still identify the decisive issue, its pleaded basis and why oral questioning is needed. Volume alone does not establish necessity.

The narrower request concerning CWP’s licensing manager and Condition 29 did not alter the outcome. That dispute likewise required a demonstrated connection to an issue the court actually needed to decide.

6. Likely Impact and Practical Significance

More focused applications

The judgment encourages parties seeking expert cross-examination to identify:

1. The precise ground and particulars engaged;
2. The conflicting affidavit passages or expert propositions;
3. The purpose for which the evidence may properly be used;
4. Why resolving the conflict matters to the outcome; and
5. Why the documents and written evidence cannot resolve it fairly.

This is the practical implication of the reasoning, rather than a new formal procedural code.

Preserving meaningful environmental scrutiny

The decision does not exclude scientific assistance from environmental judicial review. It recognises that experts may reveal omissions invisible to a non-specialist reader, and that disputed expert inferences may sometimes require oral testing.

Equally, it prevents that assistance from turning judicial review into a fresh scientific assessment conducted by the court.

Greater importance of pleading the actual complaint

A challenge to the legal relevance of environmental significance is different from a challenge asserting that effects are scientifically significant. Similarly, alleging an omitted assessment differs from contesting an assessment’s conclusion. The evidence required depends on which case has actually been pleaded.

No substantive validation of the licence

The refusal did not endorse CWP’s scientific conclusions, establish the effectiveness of Condition 29 or permit later affidavits to cure any defect in MARA’s original decision. Those questions were outside the motion’s determination.

The reserved possibility of later cross-examination also matters. In the judgment’s concluding reference to Friends of the Irish Environment v Environmental Protection Agency [2026] IEHC 415, the court preserved the trial judge’s ability to reconsider the issue if it became essential. That was a conditional safeguard, not an entitlement to repeat an unfocused application.

7. Complex Concepts Simplified

Judicial review

A court’s examination of whether a public decision was lawfully made, rather than a fresh decision on the scientific or planning merits.

Affidavit and cross-examination

An affidavit is sworn written evidence. Cross-examination allows the opposing party to question its author orally about material disputed evidence.

Primary fact and expert inference

The presence of porpoise calves is a factual matter. Predicting how survey noise will affect their survival, behaviour or habitat use involves expert inference.

Lacuna

A gap or omission. Expert evidence may expose a gap in an environmental assessment; cross-examination is not a general opportunity to repair gaps in a party’s litigation evidence.

Appropriate assessment, NIS and SAC

An appropriate assessment examines implications for a protected site. A Natura Impact Statement supplies supporting information. An SAC is a designated conservation site. This site-protection framework is related to, but distinct from, Article 12’s species-protection regime.

Derogation

A legally controlled exception to a prohibition. Blue Ireland argued that Article 16 should have been considered; the court did not decide whether a derogation was required.

Interlocutory ruling

A decision made during proceedings on a procedural or intermediate issue, without finally deciding the substantive challenge.

8. Conclusion

The judgment’s principal contribution is a disciplined test for expert cross-examination: a genuine disagreement must be connected to a pleaded issue whose fair determination requires oral testing.

It rejects both an absolute restriction to disputed primary facts and an unrestricted right to question experts whenever opinions differ. In environmental judicial review, expert evidence remains capable of exposing assessment gaps, but its use must respect the pleadings, the reviewing court’s role and the actual issues requiring decision.