Standby Letters of Credit and the Limits of the Autonomy Principle: Lessons from Celestial Aviation v UniCredit

Commercial Context

The decision of the UK Supreme Court in UniCredit Bank GmbH, London Branch v Celestial Aviation Services Ltd and Constitution Aircraft Leasing (Ireland) 3 Ltd [2026] UKSC 10 is a significant development in the law governing a Standby Letter of Credit. The case is particularly important because it examines the interaction between sanctions law and the autonomy principle, one of the foundational doctrines underpinning letters of credit and standby letters of credit.

For decades, commercial parties have relied on the principle that a Standby Letter of Credit constitutes an independent undertaking by a bank to pay upon presentation of a complying demand. The obligation of the issuing or confirming bank is generally separate from disputes arising under the underlying commercial transaction. This independence has made the Standby Letter of Credit one of the most reliable security instruments in international trade and project finance.

The Supreme Court’s decision in Celestial Aviation demonstrates that this autonomy is not absolute. In certain circumstances, public law considerations, particularly sanctions legislation, may prevent a bank from honouring an otherwise valid demand under a Standby Letter of Credit.

The Autonomy Principle

The autonomy principle provides that a letter of credit is independent of the underlying contract that gave rise to its issuance. Accordingly, a bank dealing with a Standby Letter of Credit is concerned only with whether the beneficiary has presented documents that comply with the terms of the credit.

The principle serves an important commercial purpose. Beneficiaries are assured of prompt payment without becoming entangled in disputes between the applicant and the beneficiary. Subject to limited exceptions such as fraud, the bank’s obligation to honour a compliant demand is generally regarded as absolute. This principle came under scrutiny in Celestial Aviation case.

Brief Facts of the Case

The dispute arose out of a series of civilian aircraft leasing transactions involving Irish aircraft lessors and Russian airlines. Between 2005 and 2014, the lessors entered into aircraft lease agreements with Russian carriers. As security for the lessees’ obligations, twelve letters of credit were issued between 2017 and 2020. UniCredit Bank GmbH, acting through its London branch, confirmed the letters of credit. Following Russia’s invasion of Ukraine in February 2022, the United Kingdom expanded the scope of its sanctions regime under the Russia (Sanctions) (EU Exit) Regulations 2019. The amended regulations prohibited the provision of financial services or funds in connection with arrangements involving certain restricted goods, including civilian aircraft.

Shortly thereafter, the aircraft leases were terminated following defaults by the Russian airlines. The lessors demanded payment under the letters of credit. UniCredit declined to honour the demands immediately, taking the position that payment under the credits could violate the amended sanctions regulations. The bank therefore applied for licences from the relevant UK authorities before making payment.

Although the bank subsequently obtained licences and paid the principal amounts due under the letters of credit, disputes remained regarding interest and legal costs.

The Decisions of the Courts

High Court

At first instance, the High Court held in favour of the aircraft lessors. The Court concluded that the sanctions regulations did not prohibit UniCredit from making payment under the letters of credit. Accordingly, the bank had been obliged to honour the demands when presented.

Court of Appeal

The Court of Appeal reversed the High Court’s decision. It adopted a broader interpretation of the sanctions regulations and held that payment under the letters of credit was sufficiently connected with the underlying aircraft leasing arrangements to fall within the scope of the sanctions regime.

Supreme Court

The Supreme Court unanimously upheld the Court of Appeal’s decision.
The Court held that the phrase “in connection with” contained in the sanctions regulations should be interpreted broadly. Payment under the letters of credit had a sufficient factual connection with arrangements that made aircraft available for use in Russia. Consequently, the regulations prohibited UniCredit from making payment until the necessary licences had been obtained. The Court further held that section 44 of the Sanctions and Anti-Money Laundering Act 2018 (“SAMLA”) afforded protection where a party acts on the basis of a reasonable belief that its conduct complies with sanctions legislation.

Balogun Harold Perspective

The most significant aspect of the decision is its recognition that the autonomy principle is not immune from the operation of sanctions law or in a general sense, public interest regulation. The traditional view has been that a Standby Letter of Credit exists independently of the underlying transaction. However, Celestial Aviation demonstrates that the autonomy principle operates within a broader regulatory framework. Where sanctions legislation expressly prohibits payment, a bank may be prevented from honouring an otherwise valid demand.

That said, the impact of sanctions on a Standby Letter of Credit will depend heavily on the wording of the relevant sanctions legislation. The decision turned on the broad language of the UK regulations, particularly the phrase “in connection with.” Thus different sanctions regimes may produce different outcomes depending on their statutory language and policy objectives.

The decision also has important drafting implications. It may be prudent for banks to revisit the wording of their Standby Letters of Credit and incorporate more detailed sanctions compliance provisions. Beneficiaries, on the other hand, may seek contractual protections addressing delays arising from sanctions-related licensing requirements.