The family of Harry Dunn have said they will bring a private prosecution against the Foreign Secretary, accusing him of misconduct in a public office and perverting the course of justice.

The teenager’s parents allege Dominic Raab allowed suspect Anne Sacoolas to leave the country without involving the police, while her claim for diplomatic immunity was “ambiguous”.

Charlotte Charles and Tim Dunn have also accused Mr Raab of preventing Northamptonshire Police from conducting their investigations into the 19-year-old’s death.

Mr Dunn was killed when his motorbike crashed into a car outside a US military base in Northamptonshire in August last year.

Sacoolas, the wife of an intelligence official based at RAF Croughton, was able to return to the US after claiming diplomatic immunity.

The PA news agency understands the Foreign Office (FCO) remain confident it has acted properly and lawfully in relation to Mr Dunn’s death.

In October, the Foreign Secretary told MPs the FCO had consistently called for Sacoolas’s immunity to be waived and that the police could not have lawfully prevented the 42-year-old from leaving the UK.

It is understood part of Mrs Charles and Mr Dunn’s case concerns a briefing note copied to Mr Raab’s private office three days after the crash, in which an FCO official said there was “some ambiguity in the case” concerning the suspect’s claim to diplomatic immunity.

In court documents, seen by PA, a separate briefing note from an FCO official said they had told US counterparts they would be “reserving our position” on immunity and “informing the US that we are investigating the background to the agreement”.

No-one is above the law

Procedural guidance from the Crown Prosecution Service says: “The police are responsible for establishing whether an individual or premises has diplomatic immunity.”

Sacoolas was charged with causing death by dangerous driving in December, but US secretary of state Mike Pompeo rejected an extradition request for her, a decision later described by the state department as “final”.

Speaking to PA about the decision to bring the private prosecution, Mr Dunn’s father said: “We are just normal people who have worked hard all our lives and paid our taxes.

“Like everyone else, we know that if we break the law we will have to deal with it.

“But Mr Raab appears to have felt that he is above the law and that it was OK to let Anne Sacoolas go and not tell the police about the problems with her claim to diplomatic immunity.”

He added: “No-one is above the law. We believe he has broken it and will have to face the consequences. We have already called for him to resign.

“Now he will have to account to the courts for his actions.”

A spokeswoman for the FCO said: “We have the deepest sympathy for Harry’s family. No family should have to experience what they have been through.

“The case remains of the highest priority for the Foreign Secretary who continues to raise the case with the US government.

“Both the Foreign Secretary and the Prime Minister have been clear with the US that the refusal to extradite Anne Sacoolas amounts to a denial of justice, and that she should return to the UK.

“The Foreign Secretary remains ready to meet Harry’s family and to support them to get the justice they deserve.”