Clear Interest-Variation Powers Can Authorise Benchmark Substitution, but Remain Legally Constrained

1. Introduction

This judgment addresses the circumstances in which a bank may use a standard-form variation clause to replace an agreed external interest benchmark with a rate based on its own funding costs. Although the dispute arose from commercial property lending during the financial crisis, its significance extends to contracts under which a dominant supplier reserves power to alter an essential feature of the bargain.

The Supreme Court dismissed the borrowers’ appeal. It held that the relevant clause authorised Bank of Ireland to replace EURIBOR with its Bank Cost of Funds rate. However, the Court rejected the proposition that describing a contractual discretion as “absolute” necessarily makes it uncontrolled. Such clauses require strict construction, and their exercise remains subject to limits against arbitrariness and manifest unreasonableness.

The central distinction is between whether a contractual power exists and whether an existing power has been exercised lawfully. Commercial necessity cannot supply a missing contractual power; equally, clear contractual language cannot be disregarded merely because its consequences disadvantage the customer.

2. Background and Contractual Framework

The appellants borrowed €12.2 million and €2.8 million from The Governor and Company of the Bank of Ireland in November 2009 to develop an industrial site at Rathcoole, County Dublin. The development was profitable, and the loans were repaid and the mortgage redeemed in 2017. This was therefore not a debt-enforcement or repossession case.

The offer letter described the applicable interest as a “fixed money market rate”, comprising:

• the Bank’s cost of funds;
• liquidity costs, where applicable; and
• a fixed margin initially set at 2.25% per annum.

The facilities were intended to be restructured within nine months into a single commercial mortgage repayable over 240 months, with the Bank’s margin reducing to 2%. It was undisputed that EURIBOR was the original reference rate.

Clause 5 of the incorporated standard terms provided:

“The method for calculating interest and the interest rate may be changed in respect of all facilities from time to time at the Bank’s absolute discretion, whether to take account of a change in prevailing market conventions in Ireland or otherwise. In the event of such change occurring during the continuance of this facility, the Bank will give to the Borrower one month’s prior notice that such change is to take place with effect from the date of expiry of such notice.”

In October 2011, the Bank notified the borrowers that it would move to a Bank Cost of Funds, or BCOF, basis. The change took effect after the notice period in November 2011. The borrowers objected and reserved their rights; the effectiveness of that reservation was not disputed.

They subsequently claimed that the substitution was unauthorised and had caused them to pay €738,440 in additional interest. The amount attributable to the change was undisputed. Whether that amount was recoverable depended on the proper interpretation of the contract.

3. The Issues and Procedural History

The competing interpretations

The borrowers advanced two principal arguments:

1. A power to change the “method for calculating interest” did not authorise replacement of a fundamental component of the calculation—EURIBOR—with the Bank’s own reference rate.
2. The words concerning “prevailing market conventions in Ireland or otherwise” confined the power to changes in market conventions, whether in Ireland or elsewhere.

The Bank maintained that Clause 5 expressly permitted changes to both the calculation method and the interest rate. It argued that the reference to market conventions illustrated, rather than limited, the circumstances in which the power could be exercised.

The lower courts

The Supreme Court granted leave under Article 34.5.3° of the Constitution, principally to determine the meaning of the variation clause and the limits on the Bank’s discretion: [2026] IESCDET 35.

4. Summary of the Supreme Court’s Decision

Hogan J. concluded that the appeal should be dismissed and the decisions below upheld. The essential findings were:

• Benchmark substitution fell within the clause: changing a constituent element of the interest formula was a change to the “method for calculating interest”.
• A change in market conventions was not a prerequisite: “whether” and “or otherwise” made the reference illustrative and confirmatory, not restrictive.
• Strict construction did not justify rewriting clear language: the clause’s unilateral and far-reaching character required careful scrutiny, but did not support the borrowers’ proposed interpretation.
• “Absolute discretion” remained legally constrained: courts could intervene against arbitrary or manifestly unreasonable exercise of the power.
• Contra proferentem did not apply: after ordinary interpretation, there were not two reasonably available competing meanings.

No allegation was made that the Bank’s decision was irrational, capricious or unreasonable. The decisive question was therefore the existence and scope of its contractual authority.

5. Legal Reasoning

A. Strict construction of unilateral powers

The Court recognised that Clause 5 appeared to confer sweeping power to override important elements of the parties’ agreement. Its approach nevertheless avoided two extremes: unquestioning acceptance of unrestricted discretion and automatic judicial hostility to unilateral variation clauses.

Where a standard-form contract allows a dominant contracting party to alter a fundamental feature of the bargain, courts should be slow to infer that power from doubtful or ambiguous wording. Clear words are required. That principle responds to the practical difference between a genuinely negotiated agreement and standard terms which a customer has little realistic ability to change.

The Court took judicial notice of the severe restriction in Irish retail lending in 2009 and the Bank’s dominant position in that market. This supported interpretive caution; it did not amount to a finding of a competition-law infringement or invalidate the clause.

Crucially, strict construction was not a licence to disregard the language actually used. The Court’s task remained to identify the bargain expressed by the contract, not to substitute a more balanced bargain.

B. Changing a benchmark changes the calculation method

The borrowers distinguished the calculation formula from its constituent reference-rate components. The Court considered that distinction artificial in this context. Replacing EURIBOR with BCOF altered an input which directly determined the interest payable and therefore changed the method of calculation.

The fact that the facility had originally been negotiated on a EURIBOR basis did not establish that EURIBOR was contractually immutable. The original pricing arrangements had to be read together with the incorporated variation provision.

The ruling does not establish that any contractual reference to interest variation authorises every possible restructuring. Its conclusion rests on the breadth of the particular wording, which expressly covered both the interest rate and the method for calculating interest.

C. “Market conventions” were an example, not a condition

The parties agreed that “market conventions” referred to accepted industry-wide practices, including benchmark usage and technical matters such as whether interest is calculated using a 360-day or 365-day year. They also agreed that no relevant change in market conventions had occurred.

The Supreme Court nevertheless held that the clause did not make such a change a condition of exercising the power. Its grammatical structure was decisive:

• The principal wording conferred the power to change the calculation method and rate.
• “Whether to take account of” introduced an example of a reason for exercising that power.
• “Or otherwise” confirmed that the example was not exhaustive.

Accordingly, the reference to market conventions retained a confirmatory function without restricting the power. It did not have to impose a limitation to possess contractual meaning.

The Court also rejected the suggestion that “or otherwise” should be understood as “or elsewhere”, referring only to conventions outside Ireland. Read as a whole, the clause did not support that geographical restriction.

D. Contractual authority and reasonable exercise are separate questions

The Bank’s funding difficulties explained its decision but could not independently authorise it. The evidence established that it had effectively lost access to the relevant funding market and could not obtain three-month funding at the then-prevailing EURIBOR rate of just over 0.7%.

The Court accepted that moving to a cost-of-funds basis protected the Bank’s financial interests in difficult conditions. Nevertheless, it expressly stated that reasonable conduct would be irrelevant if the contract did not confer the power exercised.

Conversely, a power expressed in broad terms did not permit arbitrary decision-making. The Court drew on authorities recognising implied limits comparable to administrative-law rationality requirements. Such a limit is not a general power for judges to substitute their preferred commercial decision.

This is an important qualification to the outcome. The Bank succeeded because the change was authorised and no irrational exercise was alleged—not because financial distress automatically permits a lender to transfer additional costs to borrowers.

E. Contra proferentem requires genuine ambiguity

The Court recognised the particular force of construing genuinely ambiguous standard terms against the party responsible for them. Had both interpretations been reasonably available, the Bank’s authorship of the clause would have strongly supported the borrowers’ interpretation.

However, the rule does not apply simply because parties disagree about meaning. The borrowers’ construction had first to be a reasonable reading of the wording. Because the Court rejected both the proposed restriction to market conventions and the distinction between a formula and its components, no residual ambiguity remained.

The judgment therefore treats contra proferentem as a response to genuine unresolved ambiguity, not as a freestanding mechanism for controlling an unfavourable contractual result.

6. Precedents Cited and Their Influence

McCord v. Electricity Supply Board

The judgment cites this authority at [1980] IRM 153 at 161, and subsequently refers to [1980] ILRM 153 at 161. Henchy J.’s discussion challenged the assumption that standard utility contracts necessarily reflect freely negotiated choices between parties dealing at arm’s length.

Its importance here was contextual and interpretive. A supplier’s power to amend standard terms unilaterally can resemble privately imposed rules more than an individually negotiated bargain. That insight supported close scrutiny of Clause 5 and explained why genuine ambiguity would carry particular weight against its drafter. It did not establish that unilateral powers are automatically unenforceable.

Law Society of Ireland v. Motor Insurers' Bureau of Ireland [2017] IESC 31, [2023] 1 IR 479

McKechnie J.’s observations concerned an agreement with substantial public-interest features and effects on third-party rights. The authority illustrated why not every contractual instrument can adequately be understood through the model of an ordinary bargain between commercial equals.

Its use was analogical. The Supreme Court did not classify the loan as a public-law contract. Rather, it placed the interpretation of standard-form powers within a wider judicial recognition that contractual context and practical bargaining conditions matter.

O'Sullivan v. Health Service Executive [2023] IESC 11

This authority supplied a more direct foundation for implied controls on contractual discretion. A contractual power to suspend a medical consultant was subject, by necessary implication, to a requirement that the decision not be unreasonable in the administrative-law sense.

The relevant principle was that contractual discretion can be constrained without converting the contract into a hybrid public-law instrument. Applied here, it supported the conclusion that the Bank’s “absolute discretion” was not an entitlement to act arbitrarily or manifestly unreasonably.

Braganza v. BP Shipping Ltd. [2015] UKSC 17, [2015] 1 WLR 1661

Lady Hale’s reasoning was cited through the discussion in the preceding Irish authority. It reinforced the proposition that the law may imply rationality-based limits into contractual decision-making powers.

Its contribution was to the control of an existing discretion, rather than to the initial construction of Clause 5’s scope. The appeal did not require the Court to examine an allegedly defective decision-making process because no irrationality challenge was advanced.

Invitel Távközlési Zrt. (Case C-472/10, EU:C:2012:242)

This decision appeared in the discussion of Directive 93/13/EEC on unfair terms in consumer contracts. Paragraph 1(j) of the Directive’s annex identifies unilateral alteration without a valid reason specified in the contract as potentially unfair.

The reference demonstrated the wider legal concern surrounding unilateral variation clauses. However, the borrowers’ agreement was expressly accepted not to be a consumer contract. Neither the Directive nor this authority supplied a direct basis for deciding its enforceability.

Investors Compensation Scheme Ltd. v. West Bromwich Building Society [1997] UKHL 28, [1998] 1 WLR 896

This authority directly supported the grammatical analysis. The wording considered there included “Any claim (whether sounding in rescission for undue influence or otherwise)…”. Lord Hoffmann treated the parenthetical expression as confirmatory rather than restrictive of the antecedent words “any claim”.

Hogan J. applied the same syntactical reasoning to Clause 5: the “whether … or otherwise” wording illustrated the preceding power without narrowing it. It also defeated the argument that the stated example established a restricted class to which the ejusdem generis principle could apply.

Pirovic v. Barbieri [2020] NSWSC 1892

The Supreme Court of New South Wales had treated “method of calculating interest” as describing the mechanical or computational features used to ascertain interest, distinct from the specification of the rate itself.

Hogan J. relied on that approach as support for treating a change to a component of the calculation as a change in method. The authority reinforced the interpretation reached from Clause 5’s language; it did not establish an independent power to substitute benchmarks.

Secondary authority

The Court also cited McDermott and McDermott, Contract Law (2017), paragraphs 10.140–10.144, for the requirement of genuine ambiguity before contra proferentem can operate.

7. Impact and Limits of the Judgment

Significance for banking disputes

The appeal was estimated to affect approximately 8,000 Bank customers. Its immediate importance lies in confirming that this wording could authorise a move away from EURIBOR without a change in market conventions.

That does not determine every customer’s position automatically. Other disputes may involve different contractual wording, incorporation questions, notice requirements, consumer protections or challenges to how a discretion was exercised.

Significance beyond banking

The judgment offers a framework for assessing standard-form powers to change essential contractual terms:

1. Identify precisely what the clause authorises.
2. Require clear wording before recognising a dominant party’s unilateral power over a fundamental term.
3. Distinguish illustrative wording from actual conditions on the power.
4. Consider separately whether the power was exercised arbitrarily or manifestly unreasonably.

The reasoning may therefore influence disputes involving other dominant service providers, while remaining sensitive to the wording and legal setting of each contract.

What the decision leaves open

The Court did not adjudicate the detailed boundaries of an irrationality challenge, because none was made. Nor did it decide a consumer unfair-terms claim, impose competition-law liability, or recognise a general financial-emergency exception to contractual obligations.

Although it upheld the Court of Appeal’s result, its reasoning focused on the clause’s broad language and implied controls on discretion. It should not be read as establishing a universal requirement that every variation clause may operate only after an external change affecting the supplier.

8. Complex Concepts Simplified

EURIBOR and BCOF

EURIBOR is an external benchmark reflecting interbank interest rates. BCOF was the Bank’s own cost-of-funds reference. Moving between them changed the basis on which the borrowers’ interest was calculated.

Strict construction

A far-reaching unilateral power must be supported by clear wording. The court scrutinises the language carefully but does not disregard an unambiguous power.

Wednesbury unreasonableness

A demanding rationality standard directed at a decision that no reasonable decision-maker could reach. It is not enough that a court would have preferred a different commercial choice.

Contra proferentem

A genuinely ambiguous contractual provision may be interpreted against the party responsible for putting it forward. An interpretation must first be reasonably available before this rule can favour it.

Ejusdem generis

A principle under which general words following specific examples may sometimes be confined to the same category. Here, the wording did not establish such a restricted category.

9. Conclusion

The Supreme Court upheld the Bank’s substitution of BCOF for EURIBOR because Clause 5 clearly authorised changes to the method of calculating interest. The reference to market conventions illustrated that power rather than conditioning it.

The broader significance is balanced: clear unilateral variation powers can be enforceable, but “absolute discretion” is not legally unlimited. Courts must scrutinise the existence of the power separately from the rationality of its exercise. Here, strict construction could not overcome clear wording, and no challenge to the reasonableness of the Bank’s decision was advanced.