The parents of Mr Dunn last month lost their court battle against the Foreign Office over whether the alleged killer of their son enjoyed diplomatic immunity.

Mr Dunn, 19, was killed in a hit-and-run in 2019 when his motorcycle was hit by a car near Croughton, Northamptonshire. The car was driven by Anne Sacoolas, wife of Jonathon Sacoolas, an operative for the CIA. With the assistance of the US government, Ms Sacoolas fled the UK and claimed diplomatic immunity from prosecution.

Judges in the High Court accepted the Foreign Office’s argument that Ms Sacoolas “enjoyed immunity from UK criminal jurisdiction”.

Mr Dunn’s parents, Charlotte Charles and Tim Dunn, have, however, been given permission to appeal.

Chief crown prosecutor for the east Midlands, Janine Smith, wrote to Mr Dunn’s family to detail the continued pursuit of Ms Sacoolas.

In her letter, she said: “I wanted to take the opportunity to provide an update following our consideration of the recent high court judgment.

“Having considered the judgment, and notwithstanding the outcome in respect of diplomatic immunity, I am satisfied that there remains sufficient evidence for a realistic prospect of conviction and that it remains in the public interest for the prosecution to continue.

“The CPS remains of the view that Mrs Sacoolas should return to the UK to stand trial.

“I do hope this confirmation is of some small comfort to Harry‘s family and friends at this challenging time of the year.”