As a Former UK military government official myself in an administrative technical capacity.
Article 41 of the Vienna convention on diplomatic relations (quoted below) clearly states: ‘do in Rome as the Romans do.’ (Respect the laws of the host state) - which applies to ALL persons under the convention and the spirit of... ‘don’t personally benefit from such protections afforded’ (Article 42). That is the general ‘spirit’ of the Vienna Convention on Diplomatic Relations.
Without prejudice to their privileges and immunities, it is the duty of all persons enjoying such
privileges and immunities to respect the laws and regulations of the receiving State. They also have a
duty not to interfere in the internal affairs of that State.
All official business with the receiving State entrusted to the mission by the sending State shall
be conducted with or through the Ministry for Foreign Affairs of the receiving State or such other
ministry as may be agreed.
The premises of the mission must not be used in any manner incompatible with the functions of
the mission as laid down in the present Convention or by other rules of general international law or by
any special agreements in force between the sending and the receiving State
The US specifically categorizes Diplomatic staff into 3 categories: diplomatic agents, technical and admin staff, and service members with applicable differences in their level of immunity. It also deals with family members separately (since technically you could class a family member as civilian)
Case law determination in the US:
“On 27 October 1998, in Vladivostok, Russia, Douglas Kent, the American Consul General to Russia, was involved in a car accident that left a young man, Alexander Kashin, disabled. Kent was not prosecuted in a U.S. court. Under the Vienna Convention, diplomatic immunity does not apply to civil actions relating to vehicular accidents, but in 2006, the U.S. Court of Appeals ruled that, since he was using his vehicle for consular purposes, Kent could not be sued civilly.
Additional citations to the consular judgement appears to be archived but can be found here: https://web.archive.org/web/20080505012445/http://vn.vladnews.ru/issue531/Crime_watch/Immunity_shelters_former_US_Consul_from_Russian_invalid https://web.archive.org/web/20080608195621/http://media.www.dailylobo.com/media/storage/paper344/news/2002/09/16/News/Russia.Student.In.Diplomatic.Controversy-274101.shtml
Whilst the provisions of the convention as mentioned at the beginning of the CPS implementation does indeed state what has been commented with here: Would diplomatic immunity allow a Consul to kill someone and get away with it?
It doesn’t as such cover publicly, and for good reason, a realistic possibility that international military establishments have special provisions/agreements which are also referenced and provisioned for, in the convention and agreed between states... I would not be at liberty to discuss the particulars of any such agreement(s), if they were to exist, for obvious reasons. There is a due expectation/requirement of respect on both parties of the convention, both receiving and sending states.
It should be appropriately noted that Consular Diplomatic Immunities are covered under a different convention, yet it provides a general idea of ‘spirit’ and use case rulings of such protections.
Consider this: It would be somewhat a serious embarrassment to international relations, if a family member (usually classed as civilian?) of any ‘diplomat’ or ‘service member’ covered by the spirit of convention to not respect the host state’s laws and to claim vehicular accidents are somehow covered?
In a further ‘use’ update to recent news regarding Harry Dunn:
Article 9 and Article 10 (b) of the convention apply. Also Article 21 and importantly Article 22, 27, 36(a) and (b) ... Article 37 to 44 says about ‘use’ quite specifically though. Though I doubt Article 43 was invoked in this case. Articles 24, 25 and 26 are likely to be relevant.
CPS guidance states regarding termination but not mentioning recall:
“Upon the termination of their functions with their mission, qualifying officers and their qualifying dependents retain their privileges and immunities in the UK for 31 days, unless otherwise advised by HMG”
A letter to notify that diplomatic immunity no longer applies, and indicating waiver requests are now irrelevant... does not as such, unless explicitly stated: waiver the immunities or privileges during the time in the UK, it is more a letter explaining jurisdiction changed due to being in a different country. (Article 32 covers waivers)
With due respect to ‘Visiting Forces’ in the UK, applicable to Ministry of Defence establishments, published an August 2016 document referred to as DSA01.1
Found here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/548060/DSA01_Defence_Policy_for_Health_Safety_and_Environmental_Protection-20160804.pdf
“5. Visiting Forces Under customary international law, Visiting Forces are not bound by domestic legislation: This is described in the Visiting Forces Act 1952. Visiting NATO Forces are subject to the Articles of the NATO Status of Forces Agreement (SOFA) 1951; of specific relevance to health, safety and environmental protection are Articles II, VII and IX. There is no similar agreement for non-NATO forces who visit, although certain aspects may be addressed in a Memorandum of Understanding; in these circumstances, normal protocol is applied bearing in mind that such Visiting Forces are covered by state immunity.
6. Interface arrangements for safety management between MOD, United States Visiting Forces and the HSE are set out in a Memorandum of Agreement, which is held on the Health and Safety website on the Defence Intranet. Enforcement action is limited to the issue of letters equivalent to Crown Notices with the recipient being an MOD employee. Similarly, there are interface arrangements for environment management between the Department, United States Visiting Forces and the EA.”
Now, as for reciprocal diplomatic immunity in the US specifically covered here: https://uscode.house.gov/view.xhtml?path=/prelim@title22/chapter6&edition=prelim
covered in section 254b of USC 22 Chapter 6 which references: (Pub. L. 95–393, §3(b), Sept. 30, 1978, 92 Stat. 808; Pub. L. 97–241, title II, §203(b)(2), Aug. 24, 1982, 96 Stat. 291.)
It states: “With respect to a nonparty to the Vienna Convention, the mission, the members of the mission, their families, and diplomatic couriers shall enjoy the privileges and immunities specified in the Vienna Convention.”
Since the complaint derives from an incident in UK territory, the US could argue that it didn’t happen on their territory. (Jurisdiction)
The only feasible recourse, in my view, would be referenced in Diplomatic Privileges Act 1964: http://www.legislation.gov.uk/ukpga/1964/81
Which references applications of the convention i.e.
“Articles 35, 36 and 40 shall be construed as granting any privilege or immunity which they require to be granted.“
“The references in Articles 37 and 38 to the extent to which any privileges and immunities are admitted by the receiving State and to additional privileges and immunities that may be granted by the receiving State shall be construed as referring respectively to the extent to which any privileges and immunities may be specified by Her Majesty by Order in Council and to any additional privileges and immunities that may be so specified.”
This recourse in particular: “Her Majesty may by an Order in Council withdraw such of the privileges and immunities so conferred from the mission of that State or from such persons connected with it as appears to Her Majesty to be proper.”
However the evidence section applies: “ If in any proceedings any question arises whether or not any person is entitled to any privilege or immunity under this Act a certificate issued by or under the authority of the Secretary of State stating any fact relating to that question shall be conclusive evidence of that fact.“
In conclusion: It is more a case of extent, application and use of such privilege or immunity for purposes that MAY or MAY NOT be connected to the functions AND performance AND transport AND even property (300-400 yards?) of the mission.