The American woman who fled the UK after teenager Harry Dunn was killed in a crash near a US military base has asked to be interviewed by British police officers in the United States under caution.

Northamptonshire Chief Constable Nick Adderley revealed the news as he urged Radd Seiger, who is acting as spokesman for the Dunn family, to “exercise constraint”.

Anne Sacoolas, the wife of a US diplomat, is believed to have been driving on the wrong side of the road when she hit 19-year-old Mr Dunn’s motorbike outside RAF Croughton in Northamptonshire on August 27.

She later fled to the US, claiming diplomatic immunity, which has since been disputed by the lawyers representing the teenager’s family.

Responding to Mr Adderley’s plea for him to exercise restraint, Mr Seiger told the PA news agency: “We are glad that he has given a press conference and we will digest what he has had to say and respond.

“But all this noise will only stop when the family sees it is going in the right direction.

“The family have lost all faith and confidence in both the police and the Foreign Office.”

Mr Seiger has accused police of ignoring the Victims’ Code, saying the Northamptonshire force had “overlooked Harry Dunn’s family’s right to be kept informed about the progress of the case”.

He said the police’s decision to delay telling the family that Mrs Sacoolas had left the country was “worrying, unacceptable and unforgivable”.

Continuing his reaction to Mr Adderley’s remarks, Mr Seiger told PA: “There is a clear breach of the Victim Code here – first and foremost they did not tell the family for a number of weeks that she had gone.

“Nothing was happening until the family and I got the ball rolling and it is no surprise that they are worried about the noise.”

Harry Dunn death
Family spokesman Radd Seiger, flanked by Harry Dunn’s mother, Charlotte Charles, and father, Tim Dunn, after meeting Foreign Secretary Dominic Raab (Jonathan Brady/PA)

After a press conference on Tuesday, Mr Adderley said the police’s work during the investigation into Mr Dunn’s death was “amongst the best I have ever seen”.

He said: “I will say, as the Chief Constable of the force, having worked in four forces previous to this, I can say that the quality and the standard of investigation that has taken place in this particular case is exemplary – is amongst the best that I have ever seen.

“I do not feel the pressure to get results on this, what I feel the pressure of is providing the very best evidence to allow the Crown Prosecution Service to make their decision and to get the relevant outcome for the family.”

Asked if he accepted the force had caused unnecessary trauma to Mr Dunn’s family by delaying telling them that Mrs Sacoolas had left the country, Mr Adderley said: “It was very much a judgment call.

“It’s a call the officers investigating the case have to make and, when we got the information on the day the waiver had been declined, so the diplomatic immunity was now applicable, it was at that time we were informed of that decision.

“It is a decision I actually support. Is it ideal that they found out through different means? No, it’s not ideal.

“But, actually, the decision to tell a grieving family is something we will reflect on and if Charlotte and Tim have been upset by that delay that is something I am prepared to apologise for – but it is a decision I would still support.”

Harry’s parents, Charlotte Charles and Tim Dunn, have made repeated pleas for Mrs Sacoolas to return to the UK to “face justice”, while Mr Seiger has accused the authorities of “further compounding the family’s misery” through “contradictory” actions.

Speaking at the press conference at the force’s headquarters, Mr Adderley said Mrs Sacoolas was “utterly devastated” and had asked to be interviewed by UK police officers in the US.

He said: “Lawyers have clearly stated that the suspect wants to be personally interviewed by officers from Northamptonshire Police in order for them to see her and the devastation this has caused her and her family.

“She did not want to provide a pre-prepared statement, which is her right to do so. We do understand from colleagues in the US that the family is utterly devastated.”

He said the force was awaiting the necessary visas before officers could travel to the US but that the suspect, whom he did not actually name, would be interviewed under caution once that could take place.

Mr Adderley went on: “From the police’s point of view, we have to make sure we maintain the integrity of all of the evidence and that it is not skewed by it (the diplomatic immunity debate) to ensure a fair trial should we get to an extradition position and she comes back to the UK.

“We don’t want to jeopardise that by not affording her a fair trial.”

Mr Adderley called on Mr Seiger to consider his behaviour.

Harry Dunn death
Harry Dunn was killed near RAF Croughton on August 27 (Family handout/PA)

He said: “I urge the family spokesman to exercise constraint in his commentary as the case moves forward. I understand the emotion and I understand the anxiety.

“I also understand the will and the want for answers to questions the family are asking.

“I have offered to go and see the family on two occasions now and on both occasions that has not been able to happen.”

He said that was due to information being requested by Mr Seiger which police were unable to share for legal reasons.

He also denied that the investigation had slowed down and said he was willing to meet the family “any place and at any time”.

“The suspect not being in the county clearly frustrates the investigation but it does not stop it,” he added.

The Dunn family are due to meet shadow foreign secretary Emily Thornberry in Westminster on Tuesday afternoon.

Harry’s mother said earlier on Tuesday that the family have been fed “one lie after another” by the British and US Governments and Northamptonshire Police.