The UK government was warned by the US embassy that the suspect in the crash which killed Harry Dunn was to leave the country.
Mr Dunn, 19, was killed when his motorbike collided with a car near RAF Croughton, Northants, on Aug 27.
Anne Sacoolas, the wife of an American diplomat, has admitted to driving on the wrong side of the road and hitting the teenager, but she returned to the US and has refused to come back.
Dominic Raab, the Foreign Secretary, told the Commons last night that the US embassy alerted them to Ms Sacoolas's "imminent" departure "unless the UK had strong objections" on Sept 13.
Police were unable to arrest Ms Sacoolas as the US had not waived her diplomatic immunity.
"We duly and immediately objected in clear and strong terms and we have done ever since," said Mr Raab.
When the Foreign Office followed up on Sept 16, the embassy said Ms Sacoolas had returned to the US.
Mr Dunn's family spokesman said the revelation "added insult to injury".
The Foreign Secretary said the case had been raised at "every level" in the US, including with Donald Trump.
In a statement, Mr Raab said: "I have already commissioned a review of the immunity arrangements of US personnel and their families at the Croughton annex I do not believe the current arrangements are right and the review will look at how we can make sure they cannot be used in this way again."
Mr Raab said diplomatic immunity for Ms Sacoolas has "clearly ended".
"There are no barriers to justice being done," in Harry's case he added.
Harry's parents were due to meet Northamptonshire Chief Const Nick Adderley on Tuesday, but cancelled because they felt he was only able to offer condolences rather than solutions.