Post‑Inquiry Updates and the Tameside Duty: Materiality Threshold for Section 36 Decisions Where ADLS Deliverability is Uncertain

Introduction

In ScottishPower Renewables (UK) Ltd v The Scottish Ministers [2026] CSOH 86, Lord Harrower (Outer House, Court of Session) refused a judicial review challenge to the Scottish Ministers’ refusal of section 36 consent (Electricity Act 1989) and deemed planning permission (Town and Country Planning (Scotland) Act 1997) for an onshore wind farm at Carrick Forest, near the Galloway Dark Sky Park.

The central controversy was not the daytime landscape impact—which the reporters regarded as broadly acceptable in policy balance—but the night-time visual effects of aviation lighting and whether those effects could reliably be mitigated by an Aircraft Detection and Obstacle Lighting System (ADLS) coupled with a Transponder Mandatory Zone (TMZ) (requiring Civil Aviation Authority engagement and airspace change processes).

The petitioner argued that, after the public inquiry and reporters’ recommendation of refusal, the Ministers had failed to inform themselves of (and failed to consider) subsequent developments relating to ADLS trials and CAA guidance, and had also acted irrationally and given inadequate reasons.

Summary of the Judgment

  • Petition refused; no reduction or declarator granted; expenses reserved.
  • The court held the Ministers did not breach the duty of inquiry: post-inquiry information relied upon by the petitioner was not materially new, and continuing uncertainty over ADLS/TMZ deliverability remained.
  • No unlawful failure to consider relevant considerations: the omitted matters were not “so obviously material” as to make non-consideration unlawful.
  • The alleged irrationality about the five-year implementation period failed: the decision letter, read fairly with the inquiry’s recommended conditions, concerned commencement within five years, not completion or prior installation.
  • Reasons were adequate under South Bucks DC v Porter (No. 2) [2004] 1 WLR 1953, especially where Ministers followed the reporters’ reasoning.

Analysis

1) Precedents Cited and Their Influence

(a) Duty of inquiry: the modern Tameside formulation

The petitioner anchored its challenge in the duty derived from Secretary of State for Education and Science v Tameside Metropolitan BC [1977] AC 1014, relying on the Court of Appeal summary in R (on the application of Plantagenet Alliance Ltd) v Secretary of State for Justice [2015] 3 All ER 261 (paras 99–100). Lord Harrower accepted that formulation as the applicable test: the question is not whether further inquiries could have been made, but whether no reasonable decision-maker could have thought the inquiries sufficient for the decision taken.

The respondents supplemented that framing with Scottish authority emphasising the restraint of review: Ibrahimi v Glasgow City Council 2026 CSIH 4 and Scottish Ministers Petitioners (Gender Recognition Reform (Scotland) Bill (Prohibition on Submission for Royal Assent) Order 2023) 2024 SC 173. The court’s approach reflects that shared premise: the duty is context-sensitive and is policed through public law standards, not by substituting the court’s preferred fact-finding.

(b) “Collective knowledge” inside government

A key forensic point was whether information known to Energy Consents Unit officials could be treated as known to the Cabinet Secretary/Ministers for decision-making. The court relied on HMRC v Tooth [2021] 1 WLR 2811 (para 70) and R (National Association of Health Stores) v Secretary of State for Health [2005] EWCA Civ 154 to reject any assumption that departmental knowledge automatically transfers to the legal “mind” of the decision-maker. That did not, however, help the petitioner on outcome, because the court held the allegedly “new” material was not materially new or decisive.

(c) Public inquiry context and procedural fairness

The respondents invoked Taylor v Scottish Ministers (No 2) 2019 SLT 681 to argue that allowing post-inquiry submissions would “distort” the Electricity Act 1989 system. Lord Harrower rejected that, holding it is common for new information to emerge after a reporters’ report—particularly where the Ministers take a long time to decide—and Ministers may need to consider whether to reopen procedures.

Importantly, the court articulated a fairness principle: if, due to new evidence/fact arising post-inquiry, Ministers become minded to depart from reporters’ recommendations, natural justice/procedural fairness would require an opportunity for representations. The court analogised to Rule 21 of the Town and Country Planning (Inquiries Procedure) (Scotland) Rules 1997. This point did not bite on the facts because the Ministers agreed with the reporters.

(d) Relevant considerations: “so obviously material” and Wednesbury

The court applied R (on the application of Friends of the Earth Ltd & others) v Heathrow Airport Ltd [2020] UKSC 52, [2021] PTSR 190 (paras 116–121). Unless statute mandates a consideration, a matter must be “so obviously material” that failure to consider it is unlawful, tested by Wednesbury irrationality. Lord Harrower used this to reject the petitioner’s attempt to recast its update-based complaints as a relevant-considerations error: the allegedly omitted items were not of the necessary obvious materiality.

(e) Reasons

On reasons, the court applied the orthodox standard in South Bucks DC v Porter (No. 2) [2004] 1 WLR 1953: intelligible and adequate reasons addressing the “principal important controversial issues,” not every material consideration, and a reasons challenge succeeds only with substantial prejudice. Following the reporters’ analysis meant an informed reader could understand the basis of refusal: continuing uncertainty as to ADLS/TMZ deliverability within an acceptable timeframe, leaving night-time effects unmitigated and unquantified.

2) Legal Reasoning

(a) Identifying the “hinge issue”: ADLS deliverability and timing

The judgment treats ADLS deliverability as the hinge on which the planning balance turned. Without ADLS, the reporters found night-time effects likely significantly adverse and inconsistent with the development plan; with ADLS, effects on the Dark Sky Park and wild land would not be significant. Hence the rationality of the refusal depended on whether uncertainty about ADLS/TMZ remained legitimate at decision time.

(b) Post-inquiry information: “new” vs “materially new”

The petitioner relied on various post-report communications (including updates about trials and anticipated guidance finalisation). Lord Harrower scrutinised the substance and concluded the information did not materially change the core uncertainties identified by the reporters:

  • Mark Hill trials: the petitioner’s own correspondence suggested slippage, revised phases, and no report until end-2025 at the earliest—supporting, not undermining, uncertainty.
  • CAP 764 (draft 7th edition): still not finalised by the Ministers’ decision date; the court rejected hindsight-based criticism given uncertainty about sign-off and potential change.
  • CAP 1616: already before the reporters; the court endorsed the reporters’ view that it aimed to simplify/expedite process rather than signal a policy shift toward granting TMZs, and also noted that speed is distinct from success.

(c) Why the Ministers were not required to “go de novo”

While the court was critical of the long delay as a practical matter, it did not accept that delay alone required the Ministers to revisit everything afresh. The lawful question remained whether it was reasonable, on the material properly treated as before the decision-maker, to proceed on the reporters’ understanding that regulatory and technical uncertainties persisted.

(d) The five-year “implementation” point: reading the decision fairly

The petitioner argued the Ministers misunderstood what needed to occur within five years—treating ADLS installation as a precondition to construction and compressing time for commencement. Lord Harrower accepted the decision letter was “not happily worded” but held that, read in context (including the reporters’ recommended conditions on commencement), the reference to five years was plainly about commencement within the usual period, not completion or pre-construction installation of ADLS. This disposed of the irrationality ground.

(e) Reasons: adoption of the reporters’ reasoning as sufficient explanation

The reasons attack failed largely because the Ministers did not introduce a new rationale. They adopted the reporters’ core finding: without sufficient assurance that ADLS/TMZ could be delivered on an acceptable timescale, night-time impacts on the Dark Sky Park would remain unacceptable in overall balance. That chain of reasoning was enough to meet the Porter (No 2) standard.

3) Impact

  • Materiality threshold for “updates” after an inquiry: the case signals that developers challenging section 36 refusals must show post-inquiry developments are not merely additional detail but materially alter the key uncertainty underpinning refusal.
  • Fairness principle when departing from reporters: the judgment clarifies that, if Ministers propose to depart from reporters due to post-inquiry new evidence or issues of fact, procedural fairness may require re-engagement with inquiry participants (with Rule 21 of the 1997 Inquiry Rules used as an analogue). Although obiter on these facts, it provides a roadmap for future disputes.
  • ADLS/TMZ disputes remain evidence-driven: the court emphasised that questions about airspace change timelines, levels, and likelihood of approval are not readily resolved in judicial review. Parties should expect that contested technical/regulatory assertions will rarely be determinative unless they translate into clear public law error.
  • Reasons challenges in section 36 cases: where Ministers align with reporters, reasons will often be upheld if the decision letter makes clear the principal controversial issue and adopts the inquiry’s logic.

Complex Concepts Simplified

  • Section 36 consent / deemed planning permission: major electricity generating stations require Scottish Ministers’ consent under the Electricity Act 1989; related planning permission can be “deemed” under the 1997 Act.
  • Suspensive condition: a condition that prevents commencement of development until specified steps are completed (here, approval of an aviation lighting mitigation plan including ADLS, after consultation).
  • ADLS: a system where turbine aviation lights activate only when aircraft are detected, reducing persistent night-time lighting.
  • TMZ: airspace in which aircraft must carry and operate a transponder/electronic conspicuity equipment, enabling detection-based lighting to be reliable.
  • Tameside duty of inquiry: a public body must take reasonable steps to obtain enough information to make its decision; courts intervene only if it was unreasonable to think the inquiry was sufficient.
  • Wednesbury irrationality: a high threshold; the decision must be outside the range of reasonable responses.

Conclusion

[2026] CSOH 86 confirms a cautious, materiality-based approach to post-inquiry developments in section 36 decision-making. Even where time has passed and the applicant has provided further updates, the Ministers do not act unlawfully unless the new material is sufficiently material that no reasonable decision-maker could ignore it, or it is “so obviously material” that fairness or legality demands direct consideration. The decision also underlines that, where Ministers adopt reporters’ reasoning on a central hinge issue—here, continuing uncertainty over ADLS/TMZ deliverability—both rationality and reasons challenges face a steep uphill task.