The US Embassy did not mention Harry Dunn’s alleged killer’s intelligence role in official notes to the Foreign Office which asserted the suspect’s diplomatic immunity, court documents show.

The first note, penned by the US Embassy three days after the crash in August 2019, only labelled Anne Sacoolas as “the spouse of a member of administrative and technical staff of the Embassy”.

But on Wednesday the Alexandria district court in Virginia was told she and her husband Jonathan Sacoolas worked for the US State Department at the time of the crash and “fled” the UK due to “issues of security”.

Mr Dunn, 19, was killed in a road crash outside US military base RAF Croughton on August 27 2019.

Sacoolas, 43, was told she was a suspect by Northamptonshire Police the following day in a meeting which was also attended by an official representing the US Embassy and State Department.

The US Embassy’s first note, dated August 30 2019, shows how diplomatic immunity was asserted on behalf of Sacoolas – eventually leading to her departure 16 days later on September 15.

The Foreign Office (FCDO) and Number 10 have both previously said the Foreign Secretary and the Prime Minister were unaware of the case until after Sacoolas had left the UK.

The suspect was eventually charged with causing Mr Dunn’s death by dangerous driving but an extradition request, submitted by the Home Office, was rejected by the US State Department in January last year.

The High Court previously ruled Sacoolas had diplomatic immunity at the time of the crash due to a loophole which meant dependants of US Embassy employees were entitled to immunity but the employees themselves were not.

The “anomaly” was closed by the FCDO in July last year.

The US Embassy referenced the loophole in its first note to the FCDO – telling UK officials “waivers of immunity must always be express” in accordance with the Vienna Convention on Diplomatic Relations.

FCDO officials were requested in the Embassy’s note “to remind appropriate authorities” not to arrest or detain Sacoolas.

The US formally declined the UK Government’s request for a waiver of immunity on September 13, two days before the suspect’s departure.

The FCDO responded to the waiver refusal by expressing its “grave disappointment” at the US’s decision on September 24 – nine days after Sacoolas had returned home.

The latest revelations have led the family to raise questions about Sacoolas’s immunity – including: “When did the British Government become aware of her real employment status?”

Their spokesman Radd Seiger told the PA news agency: “We are all still catching our breath after this astonishing revelation, having believed all this time that Mrs Sacoolas was just a dependant.

“The starting point of course is that this is not what diplomatic immunity was intended to be used for.

“But this note reveals that rather than asking itself what the right thing to do was following the tragedy, the US State Department set about looking for a way to do the wrong thing.”

Mr Seiger continued: “This note now raises some serious questions.

“Why were the US authorities less than candid with the FCO about Mrs Sacoolas’ real role whilst in the UK?

“When did the British Government become aware of her real employment status?

“Did Dominic Raab know on 28 January 2020 when Harry’s father Tim asked him point blank whether Mrs Sacoolas was working as an intelligence officer at the time of the crash, to which the response was ‘She used to work for the State Department’.”

In a hearing in which the alleged killer attempted to dismiss the Dunn family’s civil claim, her barrister John McGavin told the court he could not “completely candidly” explain why the Sacoolas family left the UK, adding: “I know the answer, but I cannot disclose it.”

US State Department spokesman Ned Price reiterated their position again on Sunday, saying: “At the time the accident occurred, and for the duration of her stay in the UK, the US citizen driver in this case had immunity from criminal jurisdiction.

“As we have said previously, the driver had diplomatic immunity because she was the spouse of an accredited staff member of the US Embassy office.”

A US official said they do not comment on diplomatic correspondence.

An FCDO spokeswoman said: “Anne Sacoolas was notified to the UK as a spouse with no official role, and the High Court determined she had diplomatic immunity while in the UK under the Vienna Convention on Diplomatic Relations.”