Fears over diplomatic immunity around Northants airbase raised 25 years before Harry Dunn's death

It's emerged that fears over a car crash involving diplomatic immunity outside RAF Croughton in Northamptonshire were first raised 25 years ago.

The High Court has refused an application by Harry Dunn's parents for theForeign Office to disclose evidence relating to a "secret agreement" betweenthe UK and US governments which is said to have given diplomatic immunity to their son's alleged killer.

Charlotte Charles and Tim Dunn are bringing legal action against ForeignSecretary Dominic Raab and Northamptonshire Police, claiming they actedunlawfully over the departure of Anne Sacoolas from the UK.

Mr Dunn, 19, was killed in August last year when his motorbike crashed into a Volvo driving on the wrong side of the road outside RAF Croughton inNorthamptonshire.

Sacoolas, whose husband Jonathan Sacoolas worked as a technical assistant at the base, claimed diplomatic immunity following the crash and was able to return to the US.

The 42-year-old was charged with causing death by dangerous driving in December but an extradition request was refused by the US the following month.

Mr Dunn's parents argue that the Foreign Office "acted unlawfully byproceeding as if Anne Sacoolas conclusively had immunity and/or advising other state bodies that she did", which they say prevented Northamptonshire Police "from reaching an informed view as to the immunity issue".

Following a preliminary hearing on Thursday, conducted remotely by video call, Lord Justice Flaux and Mr Justice Saini rejected the application for the Foreign Office to disclose further evidence ahead of a full hearing.

Lord Justice Flaux said: "We do not consider that any of the documents sought is necessary for the fair and just determination of the issues in the case, so that application is refused."

The court directed that a full hearing of Mrs Charles and Mr Dunn's case willbe heard in October or November.

Geoffrey Robertson QC, representing Mrs Charles and Mr Dunn, said the case "turns on the interpretation of a secret agreementmade in 1995, and updated in 2001, between the US and UK as a result of a US request to add up to 200 technical officers as diplomatic agents at RAF Croughton".

He said that, in 1995, the UK was "deeply concerned about this unprecedented request and the danger of media interest if crimes (in particular, road traffic-related crimes) were committed by agents and/or their dependants".

Mr Robertson wanted the court to order the Foreign Office to disclose historical documents about the 1995 agreement, as well as notes of all phone calls and other messages about Mr Dunn's death involving Foreign Office officials.

Sir James Eadie QC, for the Foreign Office, said Mr Raab "has acted lawfully at all times" and the FO had already given extensive disclosure.

The Foreign Office's lawyer said Mr Raab had acted lawfully at all times Credit: PA Images

Before the case Mr Dunn's parents released a statement saying all they wanted was for Anne Sacoolas to come back.

Harry's parents with their spokesperson outside court Credit: PA Images