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.

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.

(Harry's parents) 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

“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.