The US is refusing to send back Anne Sacoolas, who was driving the car that hit the 19-year-old’s motorbike in August – but the prime minister has urged the president to think again.

Mr Johnson hinted at the demand at the weekend when he said – after Ms Sacoolas was charged – that it was important that “the law should take its course”.

A government source told The Independent: “Of course we want her to come back. The PM has made that point to the president.”

Ms Sacoolas returned to the US after the collision, outside RAF Croughton in Northamptonshire, and subsequently claimed diplomatic immunity.

However, the Foreign Office then said her husband was not a registered diplomat and, on Friday, the Crown Prosecution Service (CPS) decided there was no immunity for dependants of consular officials.

It will now begin extradition proceedings through the Home Office, but the US may still reject the request on those grounds and the UK fears it could drag on for a long time.

On Friday, a spokesman for the US State Department said: “It is the position of the United States government that a request to extradite an individual under these circumstances would be an egregious abuse.”

And Amy Jeffress, Ms Sacoolas’s lawyer, said: “Anne will not return voluntarily to the United Kingdom to face a potential jail sentence for what was a terrible but unintentional accident.”

Bizarre: Boris Johnson drives 'Brexit' digger through boxes Show all 8 1 /8 Bizarre: Boris Johnson drives 'Brexit' digger through boxes Bizarre: Boris Johnson drives 'Brexit' digger through boxes Conservative party leader Boris Johnson drives a JCB through a fake wall POOL/AFP via Getty Images Bizarre: Boris Johnson drives 'Brexit' digger through boxes Prime Minister Boris Johnson during a visit to JCB cab manufacturing centre in Uttoxeter, while on the General Election campaign trail. PA Photo. Picture date: Tuesday December 10, 2019. See PA story POLITICS Election. Photo credit should read: Stefan Rousseau/PA Wire Stefan Rousseau PA Bizarre: Boris Johnson drives 'Brexit' digger through boxes Britain's Prime Minister and Conservative party leader Boris Johnson drives a Union flag-themed JCB, with the words "Get Brexit Done" inside the digger bucket, through a fake wall emblazoned with the word "GRIDLOCK", during a general election campaign event at JCB construction company in Uttoxeter, Staffordshire, on December 10, 2019. - Britain will go to the polls on December 12, 2019 to vote in a pre-Christmas general election. (Photo by Ben STANSALL / POOL / AFP) (Photo by BEN STANSALL/POOL/AFP via Getty Images) BEN STANSALL AFP via Getty Bizarre: Boris Johnson drives 'Brexit' digger through boxes Prime Minister Boris Johnson sits in a cab of a JCB during a visit to its cab manufacturing centre in Uttoxeter, while on the General Election campaign trail. PA Photo. Picture date: Tuesday December 10, 2019. See PA story POLITICS Election. Photo credit should read: Stefan Rousseau/PA Wire Stefan Rousseau PA Bizarre: Boris Johnson drives 'Brexit' digger through boxes Britain's Prime Minister and Conservative leader Boris Johnson drives a Union flag-themed JCB, with the words "Get Brexit Done" inside the digger bucket, through a fake wall emblazoned with the word "GRIDLOCK", during a general election campaign event at JCB construction company in Uttoxeter, Britain, December 10, 2019. Ben Stansall/AFP/Pool via REUTERS POOL REUTERS Bizarre: Boris Johnson drives 'Brexit' digger through boxes A sign made for a visit by Prime Minister Boris Johnson to the JCB cab manufacturing centre in Uttoxeter, while on the General Election campaign trail. PA Photo. Picture date: Tuesday December 10, 2019. See PA story POLITICS Election. Photo credit should read: Stefan Rousseau/PA Wire Stefan Rousseau PA Bizarre: Boris Johnson drives 'Brexit' digger through boxes Britain's Prime Minister and Conservative party leader Boris Johnson drives a Union flag-themed JCB, with the words "Get Brexit Done" inside the digger bucket, through a fake wall emblazoned with the word "GRIDLOCK", during a general election campaign event at JCB construction company in Uttoxeter, Staffordshire, on December 10, 2019. - Britain will go to the polls on December 12, 2019 to vote in a pre-Christmas general election. (Photo by Ben STANSALL / POOL / AFP) (Photo by BEN STANSALL/POOL/AFP via Getty Images) BEN STANSALL AFP via Getty Bizarre: Boris Johnson drives 'Brexit' digger through boxes Britain's Prime Minister and Conservative party leader Boris Johnson reacts as he sits in the cab of a drives a Union flag-themed JCB, after driving through a fake wall emblazoned with the word "GRIDLOCK", during a general election campaign event at JCB construction company in Uttoxeter, Staffordshire, on December 10, 2019. - Britain will go to the polls on December 12, 2019 to vote in a pre-Christmas general election. (Photo by Ben STANSALL / POOL / AFP) (Photo by BEN STANSALL/POOL/AFP via Getty Images) BEN STANSALL AFP via Getty

Instead, US officials have been negotiating to see if the Dunn family would allow the Sacoolas family to help provide a memorial for their son, as well as training to prevent similar accidents in future.

Mr Johnson’s intervention came when Mr Trump rang last week to congratulate the prime minister on his general election triumph.

Downing Street will hope that, by confronting the president on the issue, it can dilute criticism that Mr Johnson will be the US’s poodle in the post-Brexit hunt for a UK-US trade deal.

The prime minister’s spokesperson declined to confirm that he had pressed for extradition on the grounds that “this is a legal process now”.

He said: “The prime minister has discussed the case directly with President Trump on a number of occasions, including the last occasion on which they spoke.

“He said it’s important that the law should now take its course.

“This will be before the courts, but the PM has stressed on many number of occasions the importance of achieving justice for Harry’s family.”

However, the spokesperson played down suggestions of Mr Johnson meeting Harry’s family imminently.

Since the investigation into the teenager’s death was launched, the family have taken their fight to the US and even met Mr Trump at the White House.