Lawyers acting on behalf of the alleged killer of teenage motorcyclist Harry Dunn have applied to dismiss a civil claim for damages against her in the US.
Anne Sacoolas's representatives had previously admitted the 43-year-old was driving on the wrong side of the road for around 20 seconds before a fatal road crash which killed the teenager.
The PA news agency understands the Prime Minister has offered to file an "amicus brief" in the civil proceedings – meaning he would offer the court in the Eastern District of Virginia additional information it may wish to consider.
In a letter sent to the family's constituency MP Andrea Leadsom, Boris Johnson said the Government would also "fund their accommodation for the family to attend court hearings".
PA understands the Dunn family's lawyers have until December 14 to respond to Sacoolas's lawyers' application.
Their spokesman, Radd Seiger, described the motion to dismiss the civil claim as "pouring salt in the wounds", but said the parents "take comfort" from the Prime Minister's involvement in the case.
Dunn family fight for justice
Dunn family fight for justice
Undated family handout file photo of Harry Dunn. Harry Dunn's mother, Charlotte Charles, has marked the anniversary of her son's death by saying his name is "forever written into history" � and vowed to carry on his family's fight for justice.
Andrea Leadsom MP and Harry Dunn family spokesman Radd Seiger arrive to speak to the media in Brackley, Northamptonshire, where the MP called on Donald Trump to personally intervene to ensure suspect Anne Sacoolas faces trial over teenager Harry Dunn's death a year ago.
File photo dated 09/10/19 of Charlotte Charles, the mother of Harry Dunn, speaking to the media after leaving the Foreign and Commonwealth Office in London, where she met Foreign Secretary Dominic Raab. Harry Dunn's mother, Charlotte Charles, has marked the anniversary of her son's death by saying his name is "forever written into history" � and vowed to carry on his family's fight for justice.
Harry Dunn family spokesman Radd Seiger (left), Harry's mother Charlotte Charles (centre) and her partner Bruce Charles, speak with Andrea Leadsom MP (right) in Brackley, Northamptonshire, where the MP called on Donald Trump to personally intervene to ensure suspect Anne Sacoolas faces trial over teenager Harry Dunn's death a year ago.
File photo dated 20/12/19 of Harry Dunn's mother Charlotte Charles (centre) and stepfather Bruce Charles (left) outside the Ministry Of Justice in London after meeting with the Director of Public Prosecutions. Harry Dunn's mother, Charlotte Charles, has marked the anniversary of her son's death by saying his name is "forever written into history" � and vowed to carry on his family's fight for justice.
File photo dated 15/10/19 of the entrance to RAF Croughton, in Northamptonshire, near where Harry Dunn, 19, died when his motorbike was involved in a head-on collision in August last year. One year on from his death, the family of Harry Dunn continue to fight for justice in a case which has sparked diplomatic tensions between Washington and London.
File photo dated 23/04/20 of US President Donald Trump, who was told to "reconsider its position" on the immunity given to 42-year-old suspect Anne Sacoolas, following a road crash outside a US military base in Northamptonshire which resulted in teenage motorcyclist Harry Dunn's death. One year on from his death, the family of Harry Dunn continue to fight for justice in a case which has sparked diplomatic tensions between Washington and London.
Tim Dunn (far right) and his wife Tracey Dunn (second right), as they gather with friends and family at Portland Bill to scatter his son's ashes in his favourite place in Weymouth, Dorset, a month before the anniversary of his death.
File photo dated 20/12/19 of the family of Harry Dunn (left to right) mother Charlotte Charles, stepfather Bruce Charles, family spokesman Radd Seiger and father Tim Dunn. Harry Dunn's parents have dropped their legal claim against Northamptonshire Police after concluding the force are "absolved of any blame" following their son's death.
Harry Dunn's mother Charlotte Charles arrives at the Foreign and Commonwealth Office in Westminster, London, for a meeting with Foreign Secretary Dominic Raab.
Cardboard cutout of Northampton Town fan Harry Dunn who died in a car crash last August is seen in the stands during the Sky Bet League Two play-off semi final first leg match at the PTS Academy Stadium, Northampton.
Business Secretary Andrea Leadsom and Harry Dunn's mother Charlotte Charles outside South Northamptonshire Council offices in Towcester, after they met following the news that the US have refused to extradite Anne Sacoolas who is charged with causing his death in a road collision outside RAF Croughton in August last year.
A motorbike convoy makes it's way through the village of Charlton after following Harry Dunn's last ride as a tribute to the teenager who died when his motorbike was involved in a head-on collision near RAF Croughton, in Northamptonshire in August.
Charlotte Charles (left), the mother of Harry Dunn, Bruce Charles, and Tracey Dunn speak to media after a motorbike convoy followed Harry Dunn's last ride through Brackley as a tribute to the teenager who died when his motorbike was involved in a head-on collision near RAF Croughton, Northamptonshire, in August.
Chief Constable of Northamptonshire Police, Nick Adderley (centre) and Superintendent Sarah Johnson speaking during a press conference at Northamptonshire Police HQ at Wootton Hall Park, Northampton about the death of Harry Dunn.
Harry Dunn's Auntie Katie Grant (right) and Nicola Watson tie a Green Ribbons which are being made be members of the village of Charlton, Oxfordshire in memory of 19-year-old Harry Dunn who died while out riding his Green motorcycle near RAF Croughton.
Please Drive on Left signs and arrows have been placed on the B4031 road outside RAF Croughton, in Northamptonshire, where Harry Dunn, 19, died when his motorbike was involved in a head-on collision in August.
(Left to right) Bruce Charles and Charlotte Charles (Harry's mother), lawyer Radd Seiger, Tim Dunn (Harry's father) and Tracey Dunn at a press conference at the Parker New York Hotel in New York, US, where Charlotte Charles said that Anne Sacoolas, the American woman suspected of causing her son's death, should be brought back to the UK to face justice.
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Mr Dunn, 19, was killed when his motorbike crashed into a car outside US military base RAF Croughton in Northamptonshire on August 27 last year.
Diplomatic immunity was asserted by the US on behalf of Sacoolas following the collision and she was able to return to her home country, sparking an international controversy.
She was charged with causing death by dangerous driving in December last year but an extradition request was rejected by the US State Department a month later.
In his letter to Mrs Leadsom, the Prime Minister said he continued to take a "close interest" in the case.
He said: "I would like to begin by reiterating my deep condolences to Harry's family.
"They have suffered tremendous pain, which I know has been compounded by the US refusal to extradite Anne Sacoolas. I have raised this case repeatedly with President Trump, and the Foreign Secretary also discussed this with Secretary of State Pompeo during his recent visit to the US.
"I regret that there is no change in the US position."
Commenting on the civil proceedings, the letter continued: "We have separately committed to supporting the family in the civil case they have now launched in the US.
"We will fund their accommodation for the family to attend court hearings there, and are in touch with their US lawyers to understand if it would be helpful also to file an amicus brief in the proceedings.
"I continue to take a close interest in this case. I have asked the Foreign Secretary to be the lead point of contact with the family, and he will of course meet with them again as soon as there are any significant developments.
"Please let me reassure you that I am determined for this Government to do all that we can to support the efforts by Harry's family to achieve justice."
Speaking on behalf of Mr Dunn's parents about the application to dismiss the civil claim, Mr Seiger told PA: "People are judged by their actions, not words.
"Through her lawyers, but never personally, Mrs Sacoolas has talked about how devastated she is about the 'accident'. How terrible she feels.
"Harry's parents have always viewed those as mere empty words.
"Now that it is clear Mrs Sacoolas wants to also deprive them of their civil legal rights too they are forming their own conclusions and are rightly upset at this outrageous step being taken when they felt certain that this would also be the least contentious part of the dispute."
Sacoolas's legal representatives have been approached for comment.