The UK and United States have agreed to amend an "anomaly" that allowed the wife of a US intelligence official to claim diplomatic immunity following the death of Harry Dunn.
A court hearing last month heard that a "secret agreement" permitted Anne Sacoolas, who has been accused of killing Mr Dunn, to return to her home country after the 19-year-old died in a road collision outside RAF Croughton last year.
Harry’s mother Charlotte Charles said the new announcement is a "huge step forward", adding that one of the family’s aims was for this to "never happen to another family again".
She said their campaign would continue for Ms Sacoolas' return to the UK.
In a written statement following the latest announcement, Foreign Secretary Dominic Raab said: "First and foremost, the US waiver of immunity from criminal jurisdiction is now expressly extended to the family members of US staff at the Croughton Annex, thus ending the anomaly in the previous arrangements and permitting the criminal prosecution of the family members of those staff, should these tragic circumstances ever arise again.
"We have the deepest sympathy for Harry Dunn’s family," he added.
"No family should have to experience what they have gone through and I recognise that these changes will not bring Harry back.
"However, I hope that the knowledge that the Croughton arrangements have been revised and that a family in their position would now see justice done brings some small measure of comfort."
Giving his thoughts on the announcement surrounding the immunity agreements at RAF Croughton, the Foreign Secretary said: "It’s important that we have now agreed with the US new arrangements that have closed the anomaly that led to the denial of justice in the heart-breaking case of Harry Dunn.
"The new arrangements mean it could not happen again," Mr Raab added.
"I know these changes won’t bring Harry back, and I appreciate the pain and suffering the family are still going through.
"But I hope this may bring some small measure of comfort to them, because I know they want to prevent any other family going through the same ordeal they have."
The US State Department said the amendment of the diplomatic immunity arrangements at RAF Croughton "is a reflection of our especially close relationship" with the UK.
"Under the arrangement, the United States has extended pre-emptive, limited waivers of certain diplomatic immunities pertaining to the staff of the Embassy office in Croughton and their family members for acts performed outside the course of official duties that occur on or after July 20, 2020," a spokesperson said.
Cover image: Justice4Harry.