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The inviolability of diplomatic mission documents

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​A U.S. Embassy (in London) communication, purportedly recording discussions between the UK Foreign & Commonwealth Office and U.S. officials, was admissible in evidence in English court litigation against the UK government by residents of the Chagos islands. The decision is relevant to anyone involved with litigation in the English courts either against a state or where a third party state’s documents are in issue, as it provides important guidance on when a diplomatic mission’s documents may be admissible in evidence.  Here the relevant circumstances justifying admissibility included that the document was already in the public domain (it had been leaked by Wikileaks) and that it was no longer part of the London U.S. Embassy’s archive: R (on the application of Bancoult No. 3) v Secretary of State for Foreign and Commonwealth Affairs [2018] UKSC 3, 8 February 2018

A challenge of the UK government’s decision to create a Marine Protected Area

The underlying dispute in this case concerned the UK’s establishment of a Marine Protected Area (MPA) for the British Indian Overseas Territory (BIOT).  The appellant was chair of a group representing the residents of the Chagos Islands in BIOT who had been removed and resettled elsewhere by the UK government between 1971 and 1973.  The Secretary of State (SoS) established the MPA in 2010 following public consultation.  This prevented fishing in BIOT and led to the end of commercial fishing by Chagossians in the waters around BIOT.

The appellant challenged the SoS’s decision to establish the MPA.  The challenge had two limbs before the Supreme Court: (i) the decision to create the MPA had an improper ulterior motive (to make resettlement by the Chagossians impracticable); and (ii) the consultation process was flawed by a failure to disclose the arguable existence of inshore fishing rights held by Mauritius. 

Can U.S. Embassy communication be relied on? 

A sub-issue within limb (i) concerned the admissibility in evidence of a cable sent by the U.S. Embassy in London on 15 May 2009 to the departments of the U.S. Federal Government in Washington, elements in its military command structure and its Embassy in Port Louis, Mauritius (the Cable).  The Cable was published by The Guardian in 2010 and The Telegraph in 2011, apparently having been passed on by Wikileaks.  It was claimed that the Cable was a record of conversations between U.S. officials and employees of the UK Foreign and Commonwealth Office (FCO).  The appellant claimed that the Cable demonstrated that the SoS had created the MPA with the improper motive of preventing resettlement by the Chagossians. 

Inviolability of a mission’s documents – a reminder

Certain articles of the Vienna Convention on Diplomatic Relations 1961 (the Convention) form part of English law by virtue of s2(1) Diplomatic Privileges Act 1964.  These include articles 24 and 27(2), which provide, respectively, that “[t]he archives and documents of the mission shall be inviolable at any time and wherever they may be”, and “[t]he official correspondence of the mission shall be inviolable”. 

Conflicting views at first instance and Court of Appeal

The Administrative Court held that the inviolability of a mission’s documents under the Convention prevented their admission into evidence, and found that the SoS had no improper motive for creating the MPA.  The Court of Appeal held that the Cable should have been admissible but that it would not have made any difference to the Administrative Court’s conclusions on improper motive.

Supreme Court rules that Cable is admissible

The Supreme Court unanimously held that the Cable should have been admitted into evidence before the Administrative Court because it had lost its inviolability for all purposes, including its use in cross-examination or evidence in the proceedings.

Inviolability subject to qualifications

The Supreme Court held that “inviolability” under the Convention means, amongst other things, that such documents (or copies of them) cannot generally be admitted in evidence, at least in the court of the host state, unless there are extraordinary circumstances (such as state security) or an express waiver from the mission state.  There are two important qualifications:

  • the documents must constitute, or remain part of, the mission’s archive; and
  • their contents must not have been so widely disseminated in the public domain that any confidentiality or inviolability that could sensibly attach to them has been destroyed.

Cable was no longer part of a mission’s archive

There was no suggestion that the Cable published by Wikileaks had been leaked from the U.S. Embassy in London.  It had most likely come from the U.S. State Department or one of the other foreign locations to which it had been sent.  The Supreme Court held by majority that, once the Cable reached the U.S. State Department (or any other location), it was then in the custody of the U.S. Federal Government (or other relevant authority) and was not part of the London U.S. Embassy archive.  On that basis alone the Cable had lost its inviolability and was admissible.

Lord Sumption (concurring) emphasised that whether a document belonged to a mission’s archive depended on whether it was under the control of the mission’s personnel, rather than other agents of the sending state (ie the U.S.).   Lady Hale (also concurring) considered that a diplomatic communication cannot always lose its inviolability once it leaves the mission.  In her view, the concept of “control” emphasised by Lord Sumption should therefore include the restrictions placed by the mission on further transmission and use of the document (such as confidentiality markings).  However, in the present case, whatever control had initially been exercised over the Cable was clearly lost (even before it was put into the public domain by Wikileaks).

Cable was in public domain

In the Supreme Court’s view, a document can, in principle, lose inviolability where it comes into the public domain, even in circumstances where it was wrongly extracted from the mission.  The Cable had been put into the public domain by the Wikileaks publication and news articles, in circumstances where the applicant had no responsibility.  As a result, the Cable had lost its inviolability and was also admissible on this basis.

Improper motive

The Supreme Court by majority (Lord Kerr and Lady Hale dissenting) upheld the conclusions on improper motive.  The appropriate question for the Court of Appeal was whether the admission of the Cable “could” have made a difference to the Administrative Court’s conclusions on improper motive.  It had not been shown that the Court of Appeal had erred in concluding that neither cross-examination on the Cable nor the Cable itself would have led to any different outcome.

Non-disclosure of Mauritian fishing rights

The Supreme Court also rejected the appeal on the issue of alleged non-disclosure of Mauritian fishing rights.  The failure to mention Mauritian fishing rights (which had been established in a 2015 arbitral tribunal award) did not undermine the UK government’s consultation on the MPA so as to justify setting it aside. 


There is an increasing amount of litigation involving states and their organs, and also where a third party state’s documents are in issue.  This case falls into the latter category and is an example of principles of public international law and procedural aspects of domestic law (here the admissibility of documents into evidence) coming together.  The judgment makes clear that the inviolability of a mission’s documents is not absolute: inviolability can be lost where documents no longer form part of a mission’s archive or as a result of dissemination in the public domain (even if extraction from the archive was unlawful).  Where a mission wishes to preserve inviolability (including in respect of admission of documents into evidence in proceedings to which it is or is not a party), it should avoid onward transmission to multiple recipients and consider imposing restrictions on any further transmission and use.  It goes without saying that dissemination in the public domain should also be avoided, although in practice this will likely be out of a mission’s control. 

Further information

This case summary is part of the Allen & Overy Litigation and Dispute Resolution Review, a monthly publication.  If you wish to receive this publication, please contact Amy Edwards,​