British officials have formally demanded that the wife of a US intelligence officer charged with causing the death by dangerous driving of the 19-year-old motorcyclist Harry Dunn be sent back to the UK to face trial.

The Home Office has sent a request to the US government to extradite Anne Sacoolas, who has previously insisted she will not return to the UK voluntarily, over the case of the teenager who died in a collision outside RAF Croughton in Northamptonshire on 27 August last year.

A spokesman for the department confirmed the move on Friday evening, adding: “This is now a decision for the US authorities.”

However, the US state department called the request “highly inappropriate”. A department spokesman said: “The use of an extradition treaty to attempt to return the spouse of a former diplomat by force would establish an extraordinarily troubling precedent.”

A spokesman for Dunn’s family said that, while the move would not bring Dunn back, his relatives were nevertheless pleased at the extradition request and hailed it as a “huge step towards achieving justice for Harry and making good on the promise that they made to him on the night he died that they would secure justice for him”.

Timeline Harry Dunn death Show 19-year-old Harry Dunn is killed following a collision involving Anne Sacoolas, the wife of a US intelligence official. Sacoolas is believed to have been driving on the wrong side of the road when she hit the teenager riding on his motorbike outside RAF Croughton in Northamptonshire. She cooperates with police at the scene and is breathalysed. However, this first account is not treated as an interview under caution. Officers visit Sacoolas’s address, where she provides an account of events and says she had diplomatic immunity. Northamptonshire police apply for a waiver to render this void. The US embassy notifies the FCO that the spouse of a member of staff at RAF Croughton has been involved in an accident. Specially trained liaison officers are embedded with the Dunn family, including parents Charlotte Charles and Tim Dunn, and Northamptonshire police’s investigation continues in the belief they cannot detain Sacoolas. The US asserts that Sacoolas is covered by diplomatic immunity. The Foreign Office formally asks the US embassy to waive immunity. The FCO is informed by the US embassy that it will not waive immunity and she will be leaving the country, unless the UK has strong objections. However, the foreign secretary, Dominic Raab, immediately objects in “strong and clear terms”. Sacoolas leaves the UK on a US Air Force plane. The FCO approaches the US embassy and is informed Sacoolas has departed. It immediately notifies Northamptonshire police that the waiver has been declined and Sacoolas has left the UK. Officials ask police to delay telling the family by up to two days so it can decide next steps. Five days after their son's funeral, the Dunn family inform the liaison officer they have been made aware of a suggestion that Sacoolas has left the UK. Police confirm this is true. Police meet the Dunn family to officially confirm Sacoolas’s departure, and officers go through what they know. Dunn’s parents visit the White House following an invitation by US president Donald Trump. He surprises them by telling them that Sacoolas is waiting for them in an adjoining room and wishes to meet them. They decline to meet her. Harry Dunn’s father confronts the foreign secretary in his constituency, where he encourages people to vote Raab out. Video footage of the encounter emerges showing Dunn politely approaching Raab as he arrives for the hustings. The politician claimed he was happy to meet but then dismissed Dunn, adding: “Not right in front of the cameras, it’s not on.” Dunn’s family launch legal action against the Foreign Office which they said could cost them “upwards of £50,000”. Tim Dunn issues a stinging attack on Raab, accusing the foreign secretary of “empty words” and only meeting the family as a publicity stunt. “We think politicians should be honest and decent, and we feel Mr Raab is neither of those,” he writes. The Crown Prosecution Service confirms it will start extradition proceedings after Sacoolas confirms she will not return to the UK to face the charge of causing death by dangerous driving The US state department describes the extradition request as “highly inappropriate”. A department spokesman said: “The use of an extradition treaty to attempt to return the spouse of a former diplomat by force would establish an extraordinarily troubling precedent.” Home Secretary Priti Patel is informed that US authorities will not grant the British government request to extradite Anne Sacoolas. The Home Office describedsthe decision by the US secretary of state, Mike Pompeo, as a “denial of justice”. Mattha Busby and Martin Belam

The family’s spokesman, Radd Seiger, said: “Despite the unwelcome public comments currently emanating from the US administration that Anne Sacoolas will never be returned, Harry’s parents – as victims – will simply look forward to the legal process unfolding, as it must now do, confident in the knowledge that the rule of law will be upheld.

“They will simply take things one step at a time and not get ahead of themselves. However, no one, whether diplomat or otherwise, is above the law.”

In a separate interview with the BBC, Seiger said he was “100%” sure Sacoolas would return to the UK. “There is no doubt in my mind and … there never has been. Whether it’s today, or tomorrow, or in five years’ time or in 10 years, Anne Sacoolas will come back, she has to come back.”

Dunn died after his motorbike collided with a car outside the RAF base. The 42-year-old suspect claimed diplomatic immunity after the incident and was able to return to her home country, sparking an international controversy.

Dunn’s family have initiated various legal proceedings against the Foreign Office, the US government and Sacoolas herself after their lawyers disputed the granting of diplomatic immunity.

Under the treaty that exists between the two nations, the UK government is responsible for considering and forwarding extradition requests to the US state department once they have been certified by a judge.

State department officials are responsible for determining whether or not they believe the request to be “in proper order”, before it is handed over to the department of justice and the US courts. The ultimate decision on whether someone is extradited lies with the US secretary of state.