“If the CIA operated a black site on Diego Garcia, then a string of official statements, from both this and the last government, were totally false. Were ministers asleep at the wheel? Or, as the report suggests, have we been lied to for years?” The new details could be confirmed within weeks after the US Senate voted last week to declassify a 500-page summary of its three-year investigation in the CIA kidnap and torture programme that examined some six million classified documents.

A summary of the report is now with the White House which has said it is determined to release it to the public, subject to national security considerations. It remains unclear how far the CIA, which has fought bitterly against publication, will succeed in having it redacted.

The claims that the British were fully aware of a Diego Garcia black site chimes with claims by a security source to The Daily Telegraph last weekend that Tony Blair and senior government ministers, including Jack Straw, were briefed in detail and “every step of the way” on the CIA rendition programme.

Amrit Singh, senior lawyer with the New York-based Open Society Justice Initiative and the author of Administration of Torture, a book detailing the Bush administration’s torture policy, said the Al Jazeera report clearly suggested UK involvement with the CIA programme went far beyond tacit complicity.

“The fact that this says it was being done with full co-operation’ of the British government suggests that the British government knew exactly what was happening on its territory and is therefore liable for the secret detention,” she said.

The role of Diego Garcia in the CIA programme has been under scrutiny since 2006 and came back into the headlines after top secret documents found in Libya in 2011 showed Diego Garcia being listed on a CIA rendition flight plan for a Libyan Islamist Abdel-Hakim Belhadj and his wife Fatima Boudchar in March 2004.

Scotland Yard is currently investigating whether criminal charges should be laid against MI6 officers or anyone else who was complicit in the rendition of Mr Belhadj and another Libyan Islamist Sami al-Saadi who was paid a £2.2m “no fault” settlement by the British government in 2012.

After the Tripoli documents were made public by Human Rights Watch the Foreign Office issued a statement again denying that Diego Garcia had been used as a rendition stop.

“No flights with a detainee on board landed on Diego Garcia in March 2004,” said David Lidington, a minister of state at the Foreign Office, in a written parliamentary answer of December 2012 in response to a question about the Tripoli documents.

The answer added that aside from two acknowledged cases of rendition through Diego Garcia in 2002 there were “no other instances in which US intelligence flights landed in the UK, our Overseas Territories, or the Crown Dependencies, with a detainee, on board since 11 September 2001.”

In a letter to Mr Hague seen by The Daily Telegraph lawyers at Reprieve asking the foreign office both to confirm the truth of its early statements and clarify whether – if rendition flights were not allowed to land at Diego Garcia in March 2004 – it was because of concerns over earlier detentions.

Responding to the letter, an Foreign Office spokesman declined to elaborate, saying only: “I refer you to statements we’ve made in the past on this issue.”