Boris Johnson has raised the death of a teenage motorcyclist killed after colliding with a car being driven by a US citizen, with President Joe Biden.
The Prime Minister reiterated the UK wanted justice for Harry Dunn, 19, at a meeting ahead of the G7 summit.
An SUV being driven by Anne Sacoolas, allegedly crashed into Harry's motorbike outside a US military base in Northamptonshire in August 2019.
Mrs Sacoolas was charged with causing death by dangerous driving.
At his first face-to-face meeting with President Biden in Cornwall on Thursday, Mr Johnson reasserted the UK government's position on the case.
As the wife of a US intelligence official based at RAF Croughton, Mrs Sacoolas had diplomatic immunity asserted on her behalf following the crash.
Soon afterwards she returned to the USA sparking an international controversy.
The Dunn family said they were "very pleased" to see the case raised at the "first available opportunity".
"The PM raised the tragic Harry Dunn case with President Biden and reiterated that the UK wants to see justice done for the family," a No 10 spokesman said.
Speaking for the Dunn family, Radd Seiger said: "Harry's parents are very pleased to see that the PM has taken the opportunity to raise the case with President Biden at the first available opportunity.
"This rightly shows just how important this issue is and we are very grateful to the Prime Minister and his team for doing so.
"The family will continue to pursue justice until it is done," he added.
The Dunn family have challenged the diplomatic immunity asserted on Mrs Sacoolas's behalf, which will be heard before the Court of Appeal next year.
Mr Dunn's parents, Charlotte Charles and Tim Dunn, have also brought a civil claim against Mrs Sacoolas and her husband in the US state of Virginia.
Mrs Sacoolas and her husband Jonathan have been told they will be "deposed", meaning they will give their account of events under oath in front of Harry's parents.
The Crown Prosecution Service (CPS) had authorised Northamptonshire Police to charge Mrs Sacoolas with causing the teenager's death by dangerous driving, but an extradition request was rejected by the US government in January 2020.
The deposition will form part of the "discovery" process in the Dunn family's civil claim, in which correspondence and documentation relevant to the case will be handed over ahead of a trial at the end of the year.