The UK government was told the suspect in the death of Harry Dunn was a “spouse with no official role”, the prime minister’s spokesman said.
Mr Dunn, 19, died near RAF Croughton in Northamptonshire in 2019.
Anne Sacoolas claimed diplomatic immunity, and a court has heard she was employed by an intelligence agency in the US at the time of the fatal crash.
Mrs Sacoolas was charged with causing death by dangerous driving, but the US denied an extradition request.
On Thursday, the Prime Minister Boris Johnson’s official spokesman told reporters: “We don’t comment on intelligence matters.”
But he added: “She was notified to the UK Government by the US as a spouse with no official role.”
The comments about Mrs Sacoolas’ intelligence role were made at a court in Virginia, where an application to dismiss a civil claim for damages submitted by Mr Dunn’s family is being heard.
The court heard her work was “especially a factor” in her leaving the UK and she feared she would “not get a fair trial” if she returned.
When asked by the judge why Mrs Sacoolas had “fled” the UK, her barrister John McGavin said he could not respond “completely candidly”.
“I know the answer but I cannot disclose it,” he said.
Speaking after the hearing, Mr Dunn’s family’s spokesman Radd Seiger called on the UK government to “urgently reinvestigate” whether Mrs Sacoolas had diplomatic immunity.
Under the agreements at RAF Croughton dating back to 1995, anyone working at the base from the US as part of the “administrative and technical staff” would have their immunity pre-waived, meaning they would not be immune from criminal jurisdiction.
Commenting on the latest developments, the prime minister’s spokesman said: “I would emphasise that our position on this case remains unchanged, we have consistently called for her diplomatic immunity to be waived and believe that the US refusal to extradite her amounts to a denial of justice.”
US State Department spokesman Ned Price said the department had been “closely engaged with the UK government, and we have been transparent about our positions on legal and diplomatic matters” concerning the crash.
He added that Mrs Sacoolas had diplomatic immunity because she was “the spouse of an accredited staff member of the US Embassy office” at the time of crash.
Meanwhile, Labour has urged Foreign Secretary Dominic Raab to go before MPs on Friday to “explain himself”.
Shadow foreign secretary Lisa Nandy said: “Dominic Raab told MPs that [Mrs Sacoolas] she was entitled to protection as the spouse of an employee, but new information provided by her lawyer clearly indicates that she wasn’t.
“Did the foreign secretary simply accept the US Embassy’s account without asking any of the right questions on behalf of a UK citizen, or has he misled the House?”
A spokeswoman for the Foreign Office said: “The UK High Court has found that Anne Sacoolas had diplomatic immunity while in the country under the Vienna Convention on diplomatic relations.”