The death of Harry Dunn, who was struck by a vehicle allegedly driving on the wrong side of the road in August, led to a diplomatic spat over the asserted diplomatic immunity of the driver, Anne Sacoolas, the wife of a US intelligence official believed to work for the CIA based at RAF Croughton in Northamptonshire.

Diplomatic immunity, which protects its holders from civil and criminal proceedings, evolved in order to maintain diplomatic relations even in times of conflict, by ensuring that diplomats are free to go about their duties without threat of malicious interference from the courts or authorities in their host country.

Those protected by diplomatic immunity, which can include family members of the diplomat, have a duty ‘to respect the laws and regulations of the receiving state’. But there have been numerous controversial cases in which the privilege appears to have been abused. Where immunity exists, it can only be lifted in the event of a waiver from the sending state.

After several days in which the UK publicly sought a waiver from the US, it was reported that the foreign secretary had written to the Dunn family to inform them that: ‘Any question of a waiver is no longer relevant, because she has returned home…The US have now informed us that they too consider that immunity is no longer pertinent…Harry’s case is now a matter for the Northants police and the Crown Prosecution Service.’

Many people, including representatives of the Dunn family, have questioned whether Sacoolas ever enjoyed diplomatic immunity in the first place.

Whether a diplomat has immunity from criminal process in England is not a matter of discretion but a matter of law for the court to decide. The Foreign & Commonwealth Office does not confer immunity but it may provide a court deciding the issue with a certificate as to the facts upon which the court will decide whether an individual has immunity.

Under section 4 of the Diplomatic Privileges Act 1964, ‘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’.

The statements of the FCO on this matter are therefore highly significant.

Broadly speaking, there are three main situations in which diplomatic immunity might arise under the Vienna Convention: (i) where the individual is a member of a permanent diplomatic mission; (ii) where the individual is a member of a special mission which has been sent here; and (iii) where the individual is an accredited diplomat of one state and is in transit.

The Vienna Convention requires the consent of the receiving state for the appointment of the head of a permanent diplomatic mission. There is also a requirement to notify the receiving state as to ‘the appointment of members of the mission, their arrival and their final departure or the termination of their functions with the mission’. These notifications are used in order to establish entitlements to diplomatic immunity.

Diplomats who are not members of permanent missions may also enjoy immunity if they are a member of a ‘special mission’ to the UK. However, the case of R v Governor of Pentonville Prison ex parte Teja [1971] 2 QB 274 makes it plain that a UK government must still accept his appointment as a diplomatic agent.

Teja was wanted in India for fraud. He arrived on a diplomatic passport issued by the Costa Rican government and was arrested pursuant to a warrant issued by the Indian authorities. He sought to rely upon his asserted diplomatic immunity in habeas corpus proceedings. The FCO certified that Teja was not accredited as a diplomatic agent and the court rejected in terms the concept that he could be immune from criminal process by the unilateral act of the Costa Rican government in sending him to the UK. Lord Parker made the point shortly: ‘As I see it, it is fundamental to the claiming of immunity by reason of being a diplomatic agent that that diplomatic agent should have been in some form accepted or received by this country.’

A similar issue arose in the case of Khurts Bat v The Investigating Judge of the German Federal Court [2011] EWHC 2029 (Admin) in which the head of the Office of National Security for Mongolia was arrested pursuant to a European arrest warrant from Germany. Again his claim to immunity fell away following an FCO certificate.

The Vienna Convention also provides for immunity where a diplomatic agent passes through a third state in order ‘to take up or return to his post, or when returning to his own country’.

It remains unclear precisely why the FCO considered Sacoolas to have been entitled to diplomatic immunity and the letter from the foreign secretary does not take this further. The FCO has previously referred to a special arrangement reached between the UK and the US regarding the base but has not published the details of this agreement. Perhaps unsurprisingly, they have provided no further detail on the nature of her husband’s status and role in the UK.

The US position on waiver is unsurprising if hypocritical. Following a fatal car crash involving a Georgian diplomat in the US in 1997 it brought pressure to bear on Tbilisi to secure a waiver and went on to prosecute and jail the diplomat in question. The real question remains on what basis the FCO asserted that Sacoolas, the wife of an intelligence officer based in the UK, held diplomatic immunity in the first place, thus allowing her to leave the country before Northants police concluded their investigation. It remains to be seen whether the FCO will disclose its reasoning.

Thomas Garner, head of extradition, Gherson Solicitors