About 200 American staff on a military communications base in the UK were given diplomatic immunity for their roles in the US war on terrorism and the Iraq War.
The revelation has raised questions about Britain’s role in rendition and torture over the past 20 years.
Heavily redacted documents submitted to the UK government in 2006 showed British officials called for diplomatic immunity to be extended to about 200 US civilian and technical staff.
They said the move was because of the “increased demands brought on by the global war on terrorism and the war in Iraq”.
The immunity was believed to still be in place, reported The Times, which broke the news.
Reprieve, an organisation supporting the victims of human rights abuses, said the UK played a central role in enabling the rendition of suspects during the war on terrorism.
This included Libyan dissidents Sami Al Saadi and Abdulhakim Belhaj, who were detained with the help of British spies and sent to Libya, where they were tortured by the regime of Muammar Qaddafi.
The base, RAF Croughton in Northamptonshire, is of particular significance after the death of a teenager last year.
Harry Dunn, 19, was riding his motorbike when he was hit by a car driven by Anne Sacoolas, the wife of an official at the base, who fled the UK claiming she had diplomatic immunity.
“What happened to Harry Dunn was devastating,” said Maya Foa, the director of Reprieve.
“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."