The existence of a secret, CIA-run prison on the island of Diego Garcia in the Indian Ocean has long been a leaky secret in the "War on Terror," and yesterday's revelations in Time – based on disclosures by a "senior American official" (now retired), who was "a frequent participant in White House Situation Room meetings" after the 9/11 attacks, and who reported that "a CIA counter-terrorism official twice said that a high-value prisoner or prisoners were being interrogated on the island" – will come as no surprise to those who have been studying the story closely.

The news will, however, be an embarrassment to the U.S. government, which has persistently denied claims that it operated a secret "War on Terror" prison on Diego Garcia, and will be a source of even more consternation to the British government, which is more closely bound than its law-shredding Transatlantic neighbor to international laws and treaties preventing any kind of involvement whatsoever in kidnapping, "extraordinary rendition" and the practice of torture.

This is not the first time that Time has exposed the existence of a secret prison on Diego Garcia. In 2003, the magazine broke the story that Hambali, one of 14 "high-value detainees" transferred to Guantánamo in September 2006, was being held there, and in the years since confirmation has also come from other sources. Twice, in 2004 and 2006, Barry McCaffrey, a retired four-star US general, who is now professor of international security studies at the West Point military academy, revealed the prison's existence. In May 2004, he blithely declared on MSNBC's Deborah Norville Tonight, "We're probably holding around 3,000 people, you know, Bagram air field, Diego Garcia, Guantánamo, 16 camps throughout Iraq," and in December 2006 he spoke out again, saying, in an NPR interview with Robert Siegel, "They're behind bars … we've got them on Diego Garcia, in Bagram air field, in Guantánamo."

The prison's existence was also confirmed by Dick Marty, a Swiss senator who produced a detailed report on "extraordinary rendition" for the Council of Europe in June 2007 (PDF) and by Manfred Novak, the UN's Special Rapporteur on Torture, in March this year. Having spoken to senior CIA officers during his research, Marty told the European Parliament, "We have received concurring confirmations that United States agencies have used Diego Garcia, which is the international legal responsibility of the UK, in the ‘processing' of high-value detainees," and Manfred Novak explained to the Observer that "he had received credible evidence from well-placed sources familiar with the situation on the island that detainees were held on Diego Garcia between 2002 and 2003." The penultimate piece of the jigsaw puzzle came in May, when El País broke the story that "ghost prisoner" Mustafa Setmariam Nasar, whose current whereabouts are unknown, was imprisoned on the island in 2005, shortly after his capture in Pakistan – although the English-speaking press failed to notice.

Despite these previous disclosures, yesterday's article, by Adam Zagorin, is particularly striking because of the high-level nature of the source, and his admission that "the CIA officer surprised attendees by volunteering the information, apparently to demonstrate that the agency was doing its best to obtain valuable intelligence." In addition, the source noted that "the U.S. may also have kept prisoners on ships within Diego Garcia's territorial waters, a contention the U.S. has long denied."

Zagorin also spoke to Richard Clarke (at the time the National Security Council's Special Advisor to President Bush regarding counter-terrorism), who explained, "In my presence, in the White House, the possibility of using Diego Garcia for detaining high value targets was discussed." Although Clarke "did not witness a final resolution of the issue," he added, "Given everything that we know about the administration's approach to the law on these matters, I find the report that the U.S. did use the island for detention or interrogation entirely credible," and he also pointed out that using the island for interrogations or detentions without British permission "is a violation of UK law, as well as of the bi-lateral agreement governing the island."

Zagorin's source did not name the prisoners, but it seems clear that the period he was referring to ("2002 and possibly 2003") was when three particular "high-value detainees" – Abu Zubaydah, Khalid Sheikh Mohammed and Ramzi bin al-Shibh – are reported to have been held on the island, and it seems entirely plausible, therefore, that after these three were transferred to another secret CIA facility in Poland, the prison was used not only to hold Hambali, but also to hold the two other "high-value detainees" captured with him – Mohammed bin Lep (aka Lillie) and Mohd Farik bin Amin (aka Zubair). The addition of Mustafa Setmariam Nasar, who, it seems, may have been held into 2006, not only confirms that a secret prison existed, but that it was possibly in use for four years straight.

These damaging revelations seal Diego Garcia's reputation as a quagmire of injustice. A British sovereign territory – albeit one that was leased to the United States nearly 40 years ago, when the islanders were shamefully discarded by the British government and exiled to face destitution and death by misery in Mauritius – Diego Garcia has long been a source of shame to opponents of modern colonial activity. Until now, however, the only admission that any activities connected with the "War on Terror" had taken place on the island came in February, when, after years of denials on the part of the British government, David Miliband, the Foreign Secretary, finally conceded that requests for information from his U.S. counterparts had revealed that, in 2002, two rendition flights had refuelled on the island. "In both cases," Miliband stated with confidence, "a U.S. plane with a single detainee on board refuelled at the U.S. facility in Diego Garcia. The detainees did not leave the plane, and the U.S. Government has assured us that no U.S. detainees have ever been held on Diego Garcia."

The British government had been provoked to action by critics within the UK, in particular the All-Party Parliamentary Group on Extraordinary Rendition, led by the Tory MP Andrew Tyrie, and the legal action charity Reprieve, which represents 30 prisoners in Guantánamo, but the story appeared to grind to a halt when Michael Hayden, the CIA's director, stepped forward to deny that Diego Garcia had ever been used as a "War on Terror" prison.

"That is false," Gen. Hayden said when asked if a secret prison had existed on Diego Garcia, adding, as the New York Times put it, that "neither of the two detainees carried aboard the rendition flights that refuelled at Diego Garcia ‘was ever part of the CIA's high-value terrorist interrogation program.'" He also explained that one of the detainees "was ultimately transferred to Guantánamo," while the other "was returned to his home country," which was identified by State Department officials as Morocco. "These were rendition operations," he added, "nothing more."

Four weeks ago, however, the story resurfaced once more, as David Miliband reported the results of his latest request for information from his U.S. counterparts. This concerned a list of rendition flights, which, in the opinion of Reprieve and the All-Party Parliamentary Group, may also have passed through British territory, but the Foreign Secretary was confident that there was no further evidence to be mined, stating, "The United States Government confirmed that, with the exception of two cases related to Diego Garcia in 2002, there have been no other instances in which U.S. intelligence flights landed in the United Kingdom, our Overseas Territories, or the Crown Dependencies, with a detainee on board since 11 September 2001."

Yet again, the assurances of his U.S. colleagues did nothing to assuage the critics. Reprieve noted that the British government "intentionally failed to ask the right questions of the U.S., and accepted implausible U.S. assurances at face value," and added, presciently, "This remains a transatlantic cover-up of epic proportions. While the British government seems content to accept whatever nonsense it is fed by its U.S. allies, the sordid truth about Diego Garcia's central role in the unjust rendition and detention of prisoners in the so-called ‘War on Terror' cannot be hidden forever."

Just three days after David Miliband's last attempt to draw a line under the story, the British Foreign Affairs Select Committee published its latest report on the British Overseas Territories (PDF), and was scathing about Diego Garcia, declaring that "it is deplorable that previous U.S. assurances about rendition flights have turned out to be false. The failure of the United States Administration to tell the truth resulted in the UK Government inadvertently misleading our Select Committee and the House of Commons. We intend to examine further the extent of UK supervision of U.S. activities on Diego Garcia, including all flights and ships serviced from Diego Garcia."

These new revelations, of course, leave the U.S. administration looking like bald-faced liars and the British government looking like myopic dupes. Whether Michael Hayden was also duped is not known, but his strenuous denial, just five months ago, that a secret prison existed, which was manned by his own employees, will do nothing for the credibility of the U.S. administration, which likes to pretend that it does not torture and has nothing to conceal, but is persistently discovered not only being economical with the truth, but also behaving exactly as though it has guilty secrets to hide.

Whether this scandal will awaken much indignation in the American public remains to be seen, but it is hugely damaging to the British government, which is legally responsible for the activities that take place on its territory, however much it likes to hide behind "assurances" from its leaseholders that they have done nothing wrong.

It scarcely seems possible, but Diego Garcia's dark history has suddenly grown even darker.

The prisoners held on Diego Garcia

Abu Zubaydah (Zayn al-Abidin Muhammad Husayn). Saudi, b. 1971. Seized in Faisalabad, Pakistan in a joint operation by Pakistani forces and the FBI on 28 March 2002, he is regarded by the administration as a senior al-Qaeda operative and training camp facilitator, although this has been disputed by former FBI interrogator Dan Coleman, who has described him as a minor logistician with a split personality.

In February 2008, Gen. Michael Hayden, the director of the CIA, admitted that Abu Zubaydah was one of three prisoners who had been subjected to waterboarding (an ancient torture technique that involves controlled drowning) in CIA custody. Held initially in Thailand, and later in Poland, he is one of 14 "high-value detainees" transferred to Guantánamo in September 2006. At his tribunal in 2007, he denied being a member of al-Qaeda, and made a point of mentioning that he had been tortured. He has not yet been put forward for trial by Military Commission.

Khalid Sheikh Mohammed. Kuwaiti/Pakistani, b. 1964 or 1965. The supposed mastermind of the 9/11 attacks, Mohammed (commonly known as KSM) was seized in Rawalpindi, Pakistan on March 1, 2003. Like Abu Zubaydah, he was subjected to waterboarding, and is also presumed to have been held initially in Thailand, and later in Poland. Transferred to Guantánamo in September 2006, he confessed to being "responsible for the 9/11 operation, from A to Z" at his tribunal in 2007, but also made a point of mentioning that he had been tortured. He was put forward for trial by Military Commission in February, and will face the death penalty if convicted.

Rumors that KSM was held on Diego Garcia have surfaced sporadically over the years, one example being an article in the Toronto Star on July 2, 2005 (mirrored here), in which Lynda Hurst spoke to John Pike, a U.S. defense analyst. Pike, who told Hurst that he believed that KSM had been held on Diego Garcia, explained, "Diego Garcia is an obvious place for a secret facility. They want somewhere that's difficult to escape from, difficult to attack, not visible to prying eyes and where a lot of other activity is going on. Diego Garcia is ideal."

Ramzi bin al-Shibh. Yemeni, b. 1972. A friend of the Hamburg cell that led the 9/11 attacks, bin al-Shibh was seized in a raid in Karachi, Pakistan on September 11, 2002. He was reportedly intended as the 20th hijacker, but was unable to obtain a visa to enter the United States, and subsequently worked closely with KSM in planning the attacks. Transferred to Guantanamo in September 2006, he is also presumed to have been held initially in Thailand, and later in Poland, but his presence on Diego Garcia has long been suspected, because analyses of flight records have revealed that a plane flew from Pakistan to Diego Garcia immediately after his capture. He refused to take part in his tribunal in 2007, but was put forward for trial by Military Commission in February, and will face the death penalty if convicted.

Hambali (Riduan Isamuddin). Indonesian, b. 1966. Seized in Ayutthaya, Thailand in a joint operation by Thai forces and the CIA on 11 August 2003, he is regarded as the main link between al-Qaeda and its Indonesian counterpart, Jemaah Islamiyah (JI). He is alleged to have been one of the planners of the Bali bombings in October 2002, which killed over 200 people, and was transferred to Guantánamo in September 2006. At his tribunal in 2007, he said that he resigned from JI in 2000, and was not involved with al-Qaeda or with any bombings or plots. He has not yet been put forward for trial by Military Commission.

Lillie (Mohammed Nazir bin Lep) and Zubair (Mohd Farik bin Amin). Malaysians, seized with Hambali, little is known of these two men, beyond claims by the administration that they worked closely with Hambali, although they were both discussed in another TIME article, in October 2003, which examined Hambali's interrogation logs. They were transferred to Guantánamo in September 2006, but have not yet been put forward for trial by Military Commission.

Mustafa Setmariam Nasar (Abu Musab al-Suri). Syrian/Spanish, b. 1958. Seized in Quetta, Pakistan in October 2005 and handed over to U.S. forces a month later, he is not accused of being involved in direct attacks on U.S. forces, but is wanted in Spain as a witness in connection with the 2004 Madrid train bombings. Regarded as one of the most significant proponents of universal jihad, his writings include a 1600-page book, The Global Islamic Resistance Call, which was published on the internet in 2004. A critic of al-Qaeda, he reportedly fell out with Osama bin Laden in 1998, and has stated that the 9/11 attacks were catastrophic for the jihadi cause. Unlike the six prisoners mentioned above, he was not transferred to Guantánamo in September 2006, and it is not known, therefore, whether he is being held in a secret CIA prison or if he has been rendered to a third country.