Appellate Courts’ Duty to Consider State Immunity Even in the Absence of the Foreign State

Introduction

In The Royal Embassy of Saudi Arabia (Cultural Bureau) v Costantine ([2025] UKSC 9), the United Kingdom Supreme Court meticulously addressed two central issues of international and domestic significance:

Whether a domestic appellate court has an obligation under section 1(2) of the State Immunity Act 1978 (“SIA 1978”) to assess a foreign State’s claim to immunity on its own initiative, even if the foreign State does not appear at the hearing.
The correct legal test for determining when a diplomatic mission’s administrative or technical staff qualify for immunity, with additional consideration of a recent statutory amendment—the State Immunity Act 1978 (Remedial) Order (SI 2023/112).

The parties to this case were the Royal Embassy of Saudi Arabia (Cultural Bureau) (“the Embassy”) and the claimant, Mrs. Costantine, a former administrative staff member at the Embassy with Lebanese and British nationality. She alleged religious discrimination and harassment under the Equality Act 2010. The matter traveled through the Employment Tribunal, the Employment Appeal Tribunal, the Court of Appeal, and ultimately reached the Supreme Court.

Summary of the Judgment

The Supreme Court unanimously held that the Court of Appeal erred when it dismissed the Embassy’s appeal without first considering, of its own volition, whether the Embassy was entitled to invoke State immunity. Section 1(2) of the SIA 1978 imposes a mandatory duty on “any court” to give effect to State immunity, even if the State in question fails to appear. Although the Court of Appeal should have examined the immunity question itself, the Supreme Court ultimately found that immunity did not apply and upheld the Employment Tribunal’s refusal to stay or dismiss the proceedings on that ground.

As to the test for determining whether an administrative or technical staff member falls within the protective ambit of a State’s immunity, the Court reaffirmed the approach first set out in Benkharbouche v Embassy of the Republic of Sudan ([2017] UKSC 62), distinguishing between a State’s sovereign (governmental) acts and its private acts. Only those functions that are sufficiently close to the governmental functions of the diplomatic mission give rise to sovereign immunity for employment disputes.

Analysis

A. Precedents Cited

The Judgment draws heavily on existing case law, including the leading Supreme Court authority of Benkharbouche v Embassy of the Republic of Sudan ([2017] UKSC 62). In Benkharbouche, the Court ruled that certain provisions of the SIA 1978 granting immunity in all employment disputes were incompatible with both Article 6 of the European Convention on Human Rights (“ECHR”) and (for EU-derived claims) Article 47 of the Charter of Fundamental Rights of the European Union (“EU Charter”).

Benkharbouche: Confirmed that only acts carried out in the exercise of sovereign authority are entitled to immunity, and that purely “private” or commercial acts—including the employment of domestic workers—will not benefit from immunity.
Mighell v Sultan of Johore [1894] 1 QB 149: Established that at common law the court must of its own initiative recognize the position of a foreign sovereign and refuse jurisdiction if immunity applies.
Jones v Ministry of the Interior of Saudi Arabia [2007] 1 AC 270: Reiterated the principle that where State immunity applies, a national court has no jurisdiction.
United Arab Emirates v Abdelghafar [1995] ICR 65: Highlighted appellate courts’ ongoing duty to correct any failure to respect State immunity.
Sengupta v Republic of India [1983] ICR 221: An older authority that took an expansive view of immunity for embassy clerical staff, later disapproved by Benkharbouche.

International instruments such as the European Convention on State Immunity 1972 and the United Nations Convention on Jurisdictional Immunities of States and Their Property 2004 (though not yet ratified by the UK) also endorse the doctrine that courts must consider sovereign immunity on their own initiative.

B. Legal Reasoning

The Supreme Court’s path of reasoning can be distilled into two interlinked strands:

Mandatory Duty to Examine Immunity:
Section 1(2) of the SIA 1978 states that a “court shall give effect to the immunity conferred by this section even though the State does not appear.” The Court found this to be unequivocal, applying to both trial courts and appellate courts. The Embassy’s non-appearance at the Court of Appeal hearing did not relieve that court of its statutory and international obligation to determine whether immunity was properly engaged.
Narrowing the Scope of Employment Immunity:
Consistent with Benkharbouche, the Supreme Court reiterated that only employment relationships involving direct application of sovereign authority—for instance, diplomatic agents, security-sensitive roles, or employment decisions linked to a State’s political or national security prerogatives—warrant immunity. In this case, the Employment Tribunal thoroughly examined the staff responsibilities of the respondent. Despite the respondent’s formal job titles (e.g., “Post Room Clerk”, “Secretary”), none of her tasks were shown to be sufficiently proximate to heavyweight governmental functions so as to trigger immunity.

Applying this reasoning meant that although the Court of Appeal erred procedurally, there was no ultimate violation of the Embassy’s rights, since the claim for immunity would still fail on the facts.

C. Impact

This Judgment clarifies two critical points for future disputes:

Appellate Duty to Enforce Immunity: Regardless of a foreign State’s participation or non-participation, every judicial level (from first-instance tribunals to the Supreme Court) bears the duty to consider immunity if there is any suggestion that it may apply. As a result, procedural defaults on the part of the State do not automatically strip that State of the right to immunity.
Scope of Immunity for Embassy Staff: Consistent with Benkharbouche and reinforced by the Remedial Order of 2023, employees of a diplomatic mission who perform basic administrative, technical, or secretarial duties—uninvolved in governmental or sovereign policy-making—will not be covered by immunity in ordinary employment disputes. Security-related roles, positions requiring privileged access to state secrets, and matters essential to sovereign policy or recruitment will still attract immunity.

Overall, this decision both upholds the restricted (or qualified) doctrine of State immunity and ensures the availability of domestic redress for typical employment claims.

Complex Concepts Simplified

Various complex legal principles underpin this Judgment. Below are the main concepts explained in simpler terms:

State Immunity: A principle of international law stating that a foreign State cannot be sued (nor have its assets seized) before another State’s courts without its consent, subject to specific exceptions—e.g., commercial or private-law matters.
Sovereign (Governmental) vs. Private (Commercial) Acts: The dividing line is whether the conduct relates to core governmental functions (defense, security, official policymaking) or actions that any private individual or entity could undertake (e.g., routine contracts, hiring decisions unrelated to sovereign policy).
Section 1(2) SIA 1978: The statute obliging a UK court or tribunal to give effect to State immunity on its own initiative, even if the State does not appear or explicitly raise the defense.
Benkharbouche Principle: Established that blanket immunity for a diplomatic mission’s entire staff was incompatible with the right of access to courts. Immunity can only shield employment disputes that genuinely concern the exercise of governmental powers or raise national security concerns.
The Remedial Order (SI 2023/112): An amendment designed to bring the SIA 1978 into compliance with the Supreme Court’s guidance in Benkharbouche. It clarifies that only diplomatic agents (and certain sensitive positions) are fully covered by immunity.

Conclusion

The Supreme Court’s ruling in The Royal Embassy of Saudi Arabia (Cultural Bureau) v Costantine ([2025] UKSC 9) is significant for underscoring the mandatory nature of section 1(2) of the SIA 1978 at every judicial level, including appellate jurisdictions—an appellate court, just like a court of first instance, must ensure compliance with immunity obligations. Nonetheless, the Court found that, on the specific facts of this case, State immunity did not apply to the respondent, given her routine administrative duties.

Taken overall, this decision affirms the narrower contours of employment-related immunity, ensuring that individuals engaged in non-sovereign activities at embassies can seek redress in domestic courts. It further cements the “restrictive” doctrine of immunity in the UK, which focuses on distinguishing between commercial or private acts and actual sovereign operations. This balancing act respects the international law obligation of par in parem non habet imperium (sovereign equality of States) while also safeguarding the rights of employees serving in typical administrative or support roles within diplomatic missions.