The family of Harry Dunn, the teenager killed in a motorcycle crash, are launching three separate legal actions against the Foreign Office, Northamptonshire police and Anne Sacoolas, the American wife of a US intelligence officer who has admitted to driving on the wrong side of the road before the collision.

Tim Dunn, the father of Harry, said that after consultation with their lawyers the family felt they had reached “the end of the road” with their efforts to persuade Sacoolas to return to the UK and face a police investigation, and so needed to embark on a series of legal actions.

The Dunn family will launch a judicial review into how the FCO accepted Sacoolas’s claim for diplomatic immunity and then failed to tell them that she had left the country.

The FCO said it was not informed by the US embassy until 16 September that she had left the country on a US military plane the day before, and the family were not informed of this for a further 10 days. The Foreign Office has held only one meeting with the Dunn family since the accident on 27 August, Tim Dunn told LBC on Friday morning.

The judicial review will also examine the US-UK exchange of notes dating back to 1995 that, according to the FCO, waived diplomatic immunity for staff at RAF Croughton base but not for their spouses – an apparently untested arrangement that the FCO has admitted is anomalous. Sacoolas was married to Jonathan Sacoolas, who worked at the base.

The family has also referred Northamptonshire police to the Independent Office for Police Conduct (IOPC) over its role in allowing Sacoolas to leave the country. The police have insisted it would not in retrospect do anything differently.

Finally, the family are trying to launch civil proceedings against Sacoolas in a US court. A lawyer for the Dunn family, Radd Seiger, is due to travel to the US to discuss such an action with lawyers. He is being advised by two leading human rights lawyers, Geoffrey Robertson and Mark Stephens.

Seiger said: “We did not want to get this legal ball rolling. It’s absolutely clear that Ms Sacoolas was involved in a very serious collision that ended in the loss of Harry’s life.

“We are clear she’s admitted her culpability, that she … committed a very serious crime that night.

“At the very least careless, causing death by careless driving, and at the worst causing death by dangerous driving. She is a fugitive from this country and she is on the run.

“We appeal to her to come back to this country and face the music.”

Separately, Northamptonshire police has applied for visas to travel to the US to see if they can meet Sacoolas, interview her under caution and persuade her to return to the UK to face a police investigation.

She has expressed deep remorse at Harry Dunn’s death, but insisted she will not return, leaving Tim Dunn to claim that Northamptonshire police’s trip to the US was “little more than a PR stunt”.

The US state department has said diplomatic immunity is “no longer pertinent” now that she is back in the US, but has not said whether it intends to allow a prosecution in the US.

An extraordinary effort by President Donald Trump to engineer a reconciliation meeting between the Dunn family and Sacoolas in the White House ended in failure after they rejected Trump’s attempt.

An FCO spokeswoman said: “We have done everything we can properly to clear a path so that justice can be done for Harry’s family.

“As the foreign secretary set out in parliament, the individual involved had diplomatic immunity whilst in the country under the Vienna Convention on Diplomatic Relations.”