The Prime Minister says the refusal to grant an extradition request for the suspect charged in connection with the death of Harry Dunn is a “denial of justice”.
Boris Johnson’s words have been welcomed by the teenager’s mother, Charlotte Charles, who told the PA news agency they are “words that need action behind them”.
Mr Johnson is the latest senior government figure to criticise the US secretary of state’s decision to reject the request for the return of Anne Sacoolas to the UK – following in the footsteps of the Foreign Secretary and the Home Secretary.
On Monday, the Prime Minister’s spokesman told a Westminster briefing: “We believe that this is a denial of justice and the individual concerned should return to the UK.”
The Prime Minister also “reiterated the need” for Mrs Sacoolas to return to the UK during a phone call with US President Donald Trump on Friday.
Mr Dunn was killed when his motorbike crashed into a car outside a US military base in Northamptonshire on 27 August last year.
Mrs Sacoolas, 42, the wife of a US intelligence official based at RAF Croughton, was granted diplomatic immunity after the crash, sparking an international controversy.
US secretary of state Mike Pompeo rejected an extradition request by the UK Government for Mrs Sacoolas on Thursday.
Reacting to Mr Johnson’s comments, Mrs Charles told PA he needs to “use his power” to put the pressure on Mr Trump and Mr Pompeo to send the suspect back to the UK.
She said: “The fact that he has come out and said that is obviously a good thing but we hope that he can follow this up with actions now.
“He needs to use his power, because he’s the only person with the power to tell Trump and Pompeo that she needs to come back.
“It feels good that he’s on the same page as us and this is certainly a step in the right direction.”
Asked what her message to the Prime Minister would be, Mrs Charles told PA: “Make the country proud of you. There are a lot of people out there who don’t necessarily have faith in this government and this is a chance for him to restore a bit of that faith.
“It’s certainly another step forward but until I see action, they are not empty words, but they are words that need action behind them to show us that they are 100% going to stand up for us.”
Foreign Secretary Dominic Raab is set to hold a “vitally important meeting” with Mrs Charles and the rest of Mr Dunn’s family on Monday.
Mr Dunn’s parents have said they are confident talks with Mr Raab will be “constructive and productive” – adding that it is “more important now than ever” to be on the same page.
Mrs Charles and Mr Dunn’s father, Tim Dunn, have disputed the Foreign Office’s claim that the suspect had diplomatic immunity at the time of a road crash.
The teenager’s parents have said they expect the Foreign Secretary to make it clear there will be “severe consequences” if the US government continues to refuse to return Mrs Sacoolas after their meeting.
Mr Pompeo is set to have a meeting with Mr Raab on Wednesday.