Date: Jul 9, 2026

Costs of Moot Interlocutory Motions: Where the Merits Will Be Tried, Costs Should Generally Be “In the Cause”

1. Introduction

In Association Of Optometrists Ireland and Ors v Minister For Social Protection and Ors [2026] IEHC 435, O'Connell J addressed the costs consequences of an interlocutory motion that became moot before it was determined. The plaintiffs were a professional representative body for optometrists and two optometrist plaintiffs. The defendants were the Minister for Social Protection, the Minister for Health, and the Health Service Executive.

The motion sought an order compelling completion of consultations under s.42 of the Public Service Pay and Pensions Act 2017 relating to fees payable under the Treatment Benefit Scheme (TBS). While the proceedings were ongoing, the Minister for Social Protection made S.I. No. 24 of 2026 (the 2026 Regulations), which in practical terms delivered the motion’s objective. The interlocutory motion therefore became moot, but the underlying plenary action (including damages and quantum meruit claims) remained for trial.

The central issue for the High Court was how to allocate the costs of a moot interlocutory motion where the same alleged wrong (delay/failure under s.42) would be adjudicated at trial.

2. Summary of the Judgment

The Court held that, because the interlocutory motion overlapped directly with issues that remained to be tried in the substantive action (notably alleged unlawful delay/failure and resulting loss), it would be unjust to decide the motion’s costs finally at this stage.
The appropriate order as between the plaintiffs and the Minister for Social Protection was that the costs of the interlocutory motion be “costs in the cause”.
No separate costs order was made in favour of the Minister for Health, notwithstanding that the relief could not have been ordered against her, because this point did not generate meaningful additional controversy or cost.

3. Analysis

3.1 Precedents Cited

(a) Hughes v Revenue Commissioners [2023] 3 IR 393: the modern framework for mootness and costs

O'Connell J adopted Murray J’s structured treatment of costs where proceedings become moot, summarising three “broad propositions”:

If mootness arises from circumstances outside either party’s control, generally no order for costs.
If mootness arises from a unilateral act of a party, generally costs are awarded against that party.
For statutory bodies, the court must be cautious: the ordinary exercise of statutory functions may render a case moot without being a “concession” to litigation; the statutory body should adduce evidence showing the change was not driven by the proceedings.

Critically, the High Court treated this as a starting point, but not a complete answer, because the present case concerned a moot interlocutory motion within a still-live plenary action.

(b) Dubcap Ltd v Microchip Ltd (Unreported, Supreme Court, 9 December 1997), AIB v Diamond (Unreported, High Court (Clarke J), 7 November 2011), and ACC Bank plc v Hanrahan [2014] 1 IR 1

These authorities were used for the proposition that where interlocutory relief is decided on a provisional basis (without a final merits determination), the just course is typically to reserve costs or make them costs in the cause. The judgment emphasises that this is not mere procedural tidiness: it avoids the injustice of fixing costs by reference to an interlocutory snapshot where the final outcome may diverge materially.

(c) Keogh v AV Pound Co. Ltd [2021] IEHC 640: moot interlocutory injunctions where the core dispute remains

Keogh was central. There, the plaintiff’s suspension was lifted before the injunction motion was heard. Allen J refused to speculate about what would have happened on the motion, and ordered costs in the cause because the substantive lawfulness dispute remained for trial and would be the proper context to allocate responsibility for costs.

O'Connell J applied the same logic: where a motion becomes moot before hearing, and the same factual/legal issues will be revisited at trial, the trial judge will be best placed to decide whether the motion was necessary and who should bear its costs.

(d) Naughton v Governor and Company of the Bank of Ireland [2025] IEHC 124: distinguished

The plaintiffs relied heavily on Naughton, where costs of a moot interlocutory injunction were awarded to the plaintiff. O'Connell J distinguished it on two “critical” grounds:

In Naughton the defendants’ steps rendered moot both the interlocutory motion and the entire substantive action, so there would be no trial to provide a better basis for costs allocation.
The court in Naughton made express findings on the balance of probabilities about the receiver’s lack of power—findings not going to be revisited at any trial—whereas in the present case any view of unlawfulness/delay would necessarily be provisional and overlapping with issues for trial.

This distinction matters because it identifies when a court may properly determine costs now (where merits findings are final and will not be revisited), versus when it should refrain (where merits findings are incomplete or would pre-empt the trial).

(e) Cunningham v. President of the Circuit Court [2012] 3 I.R. 222 and Godsil v. Ireland [2015] 4 I.R. 535

These cases appeared via the discussion in Keogh. They are examples where the substantive dispute became moot, altering the costs analysis because the court would never determine the merits at trial. O'Connell J’s use of Keogh indicates that reliance on “mootness costs” authorities is more persuasive when the entire dispute has evaporated than where only an interlocutory step has become unnecessary.

3.2 Legal Reasoning

(a) A key structural distinction: moot actions vs moot interlocutory motions

The judgment articulates a practical taxonomy:

Type 1 motions: discrete interlocutory applications that will not be revisited at trial (e.g. pleadings defaults, particulars, discovery). Here, applying the “moot proceedings” costs principles is relatively straightforward.
Type 2 motions: interlocutory relief that is inherently provisional and overlaps with ultimate merits (classically, interlocutory injunctions or mandatory orders pending trial). Here, costs should usually await the trial outcome.

The motion in this case fell into Type 2: it sought a mandatory interlocutory order to advance the very process whose alleged unlawfulness/delay grounded the remaining damages claim.

(b) Why the making of the 2026 Regulations was not treated as an “admission”

The plaintiffs argued that because the motion’s objective was achieved by the making of the 2026 Regulations, costs should follow. The Court rejected treating that event as conclusive because:

The Minister for Social Protection contended the consultation had concluded earlier and that the subsequent regulations were part of the statutory decision-making pathway, not a capitulation.
The plaintiffs contended the regulations vindicated the necessity of the proceedings—an issue that overlaps with the alleged wrong.

Because these competing narratives go to the heart of liability and causation in the damages claim, deciding costs now would risk prejudging the merits.

(c) The operative fairness principle: allocate costs when the court can do so on the best evidential footing

The Court’s core fairness concern was “risk of injustice”: deciding costs on an interlocutory record could force the court into (i) speculation as to what would have happened had the motion been argued, and/or (ii) premature adjudication of disputed factual issues that will properly be tested at trial (pleadings, discovery, oral evidence). Hence, costs were made in the cause.

(d) Treatment of the Minister for Health’s costs

Although the Court accepted the interlocutory relief could not have been ordered against the Minister for Health, it declined to make a separate costs order in her favour. The reasoning was pragmatic: the point was straightforward, raised by the same legal team, and did not measurably add to the motion’s cost or complexity. This illustrates that “misjoinder for interlocutory relief” does not automatically yield a discrete costs entitlement absent demonstrated incremental cost or controversy.

3.3 Impact

Clarifies costs practice for moot interlocutory relief in ongoing plenary actions: where the interlocutory motion concerns issues that will be determined at trial, the default “just” order is likely to be costs in the cause, even if a later supervening event delivers the practical objective of the motion.
Reinforces Keogh’s anti-speculation approach: courts should avoid mini-trials about what would have happened on an unargued motion, or about whether the opponent’s later conduct was truly “unilateral” in the Hughes sense, when trial findings will soon be available.
Limits reliance on Naughton: parties seeking immediate costs after mootness should expect close scrutiny of whether the substantive action is also moot and whether the court can make final merits findings that will not be revisited.
Practical message for public-law-adjacent commercial/statutory disputes: the making of regulations or administrative steps during litigation will not automatically translate into an adverse costs order for the public authority where the authority maintains the steps were part of the statutory process and damages/merits issues remain live.

4. Complex Concepts Simplified

Mootness: A case (or an application) is “moot” when a later event means the court’s decision is no longer needed to resolve the immediate dispute (e.g., the sought-after regulation is made). The key question becomes what to do about costs.
Interlocutory relief: Temporary or interim court orders made before trial (often on affidavit evidence) to manage the situation pending a full hearing. Because the court does not finally decide the merits, costs decisions based on interlocutory outcomes can be unreliable.
“Costs in the cause”: The costs of the interlocutory motion will follow the eventual winner of the overall action (the “cause”). It postpones the costs decision until the court can assess who was truly justified, in light of the final merits.
“Unilateral act” and statutory bodies (Hughes): If one party acts alone in a way that moots proceedings, costs may fall on that party. But where the party is a statutory decision-maker, an action taken in the ordinary discharge of statutory powers/duties is not automatically treated as a litigation-driven concession.
Provisional merits tests on interlocutory applications: Interlocutory injunctions commonly turn on whether there is a “fair/serious issue to be tried” (or, in some contexts, a “strong case”). These are not final findings of right or wrong, which is why allocating costs definitively at this stage can be unfair.

5. Conclusion

[2026] IEHC 435 strengthens a coherent rule of thumb: when an interlocutory motion becomes moot but the substantive action continues and the same dispute will be determined at trial, the fairest course is typically to make the motion’s costs costs in the cause. The judgment integrates the mootness-costs framework in Hughes v Revenue Commissioners [2023] 3 IR 393 with the interlocutory-costs caution in Keogh v AV Pound Co. Ltd [2021] IEHC 640, and confines Naughton v Governor and Company of the Bank of Ireland [2025] IEHC 124 to cases where the substantive dispute has also evaporated or where the court can make final merits findings that will not be revisited.