Mr Dunn 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.

The documents show that, in 1995, 2001, and 2006, Foreign and Commonwealth Office officials made a case to ministers to extend diplomatic immunity – including providing immunity from criminal prosecution – to an estimated 200 staff working at the RAF Croughton base in Sussex, where Ms Sacoolas lived at the time of the incident which killed Mr Dunn.

The heavily-redacted documents include a ministerial submission from 2006 which identifies the base’s role in ‘war on terror’ operations as a reason for granting bulk immunity. This 2006 submission to ministers notes the “increased demands brought on by the global war on terrorism and the war in Iraq” and raises a concern that granting bulk diplomatic immunity to multiple US staff would provoke a “possible read-across by the media to rendition flights”.

Ms Sacoolas claimed diplomatic immunity in order to avoid trial. The Dunn family is challenging the Foreign Office’s role in allowing Ms Sacoolas to leave the country.

Maya Foa, Reprieve’s director, said: “What happened to Harry Dunn was devastating. His family should never have had to go through this, and we extend our deepest sympathies to them.

“The shockwaves of the worst of the ‘war on terror’ have been felt for far too long. Only by fully investigating this dark part of British history can we hope not to make the same mistakes again. We need an independent, judge-led inquiry into the UK involvement in torture and rendition’.”