The lawyers of Harry Dunn’s family are set to launch a judicial review into the Foreign Office’s advice to grant diplomatic immunity to a woman accused of killing him in a crash.
Anne Sacoolas, 42, who is reportedly married to a US intelligence official, left the UK just days after the collision which left the 19-year-old motorcyclist dead on August 27.
The motorist allegedly collided with the teenager.
Harry’s mother, Charlotte Charles, and the teenager's father, Tim Dunn, said they felt let down by the decision to allow Ms Sacoolas - to flee after the collision outside RAF Croughton in Northamptonshire.
The family's spokesman Radd Seiger said that their lawyers, Mark Stephens and Geoffrey Robertson QC, are now prepared to launch a full investigation into the FCO over their involvement in the decision to grant immunity to Mrs Sacoolas.
Mr Seiger said: "What Mark and I are going to do, is we are going to write to the FCO very shortly, explaining that we don't want to do a judicial review, but to avoid that please let us have the following documents - all e-mails, messages, notes in relation to your advice to Northamptonshire Police that this lady had it (diplomatic immunity).
"What we don't know is whether somebody cocked up or whether they were put under pressure by the Americans to concede.
"We want to conduct an investigation into the FCO's decision to advise Northamptonshire Police that this lady had the benefit of diplomatic immunity.
"If we're not satisfied, then we'll go to a judicial review and ask a High Court judge to review it all."
Speaking at a press conference in New York on Monday, Tim Dunn said: Mr Dunn added: "Somewhere, somebody has made a decision to give this lady immunity.
"She's not entitled to immunity as it's been said and we've known that from the start.
"They made a mistake, someone has made a mistake."
