THE family of Harry Dunn declared that the US government has started “a battle it’s not going to win” after it refused to extradite the person driving the car that killed him last summer.

Mr Dunn was 19 when his motorbike collided head-on with a car that was being driven on the wrong side of the road — according to a police investigation — near RAF Croughton in Northamptonshire in August.

The suspect, Anne Sacoolas, who is married to a US National Security Agency spy, claimed diplomatic immunity when questioned by police and later left the country on a US Air Force aircraft.

The Dunn family’s lawyers advised that Ms Sacoolas was not entitled to immunity as Mr Sacoolas was not listed as a diplomat.

The Crown Prosecution Service announced last month that she would be charged with causing death by dangerous driving.

Mr Dunn’s parents, Charlotte Charles and Tim Dunn, were informed of US Secretary of State Mike Pompeo’s decision to refuse Ms Sacoola’s extradition in a call with their MP, Andrea Leadsom, on Thursday.

In a statement, the US State Department said that at the time of the accident, and for the duration of her stay in Britain, the US citizen had immunity from criminal jurisdiction.

A spokesman said that if the US was to fulfil the extradition request it would “set an extraordinarily troubling precedent” and would render diplomatic immunity practically null.

Mr Dunn’s parents have said they are “not surprised” by the decision, but added that it will “not be a battle the US government is going to win.”

Foreign Secretary Dominic Raab said the “UK would have acted differently” and that the decision “amounts to a denial of justice.”

Although the Foreign Office maintains that Ms Sacoolas had diplomatic immunity, Mr Raab said he would look to “resolve the issue” surrounding any immunity given to staff at the RAF base.

The Dunn family’s lawyers said was the first time in the 100-year history of the extradition treaty that such a request had been turned down by the US.

Business Secretary Ms Leadsom met with US ambassador Woody Johnson, the commander of RAF Croughton Colonel Bridget McNamara and the Chief Constable of Northamptonshire Police yesterday at an undisclosed location.