The UK government is facing renewed pressure to make a full disclosure of its involvement in the CIA’s post-9/11 kidnap and torture programme after another leading Bush-era US official said suspects were held and interrogated on the British territory of Diego Garcia.

Lawrence Wilkerson, who was chief of staff to Colin Powell at the US state department, said the Indian Ocean atoll was used by the CIA as “a transit site where people were temporarily housed, let us say, and interrogated from time to time”.

In an interview with Vice News, Wilkerson said three US intelligence sources had informed him that the CIA used Diego Garcia for what he described as “nefarious activities”, with prisoners being held for weeks at a time.

“What I heard was more along the lines of using it as a transit location when perhaps other places were full or other places were deemed too dangerous or insecure, or unavailable at the moment,” said Wilkerson, who served under Powell from 2002 to 2005.

“So you might have a case where you simply go in and use a facility at Diego Garcia for a month or two weeks or whatever and you do your nefarious activities there.”

Donald Campbell, spokesman for the legal rights group Reprieve, said: “We already know Diego Garcia was used for CIA renditions, yet over a decade on the British government has yet to own up to the full part the island played in the CIA’s torture programme.

“Ministers have consistently claimed that no CIA detainees were held on the island, but Col Wilkerson’s account suggests that either they are lying or they have been lied to. It is high time the British government came clean over the part UK territory played in the CIA’s shameful torture programme.”

Diego Garcia’s population was removed during the late 1960s and early 70s and forced to settle on the Seychelles and Mauritius. Since then the atoll has been leased by the UK to the US for use as a military base.

Wilkerson is the latest of a number of well-placed officials who have said that after 9/11 the atoll was also used in the CIA rendition programme.

Barry McCaffrey, a retired four-star American general, has twice spoken publicly about the use of Diego Garcia to detain suspects.

Manfred Nowak, a former United Nations special rapporteur on torture, has said he has heard from reliable sources that the US held prisoners on ships in the Indian Ocean.

Dick Marty, a Swiss senator who led a Council of Europe investigation into the CIA’s use of European territory and air space, said he received confirmation of the use of the atoll. He later said he received the assistance of some CIA officers during his investigation.

There also is a wealth of circumstantial evidence to suggest that Diego Garcia was used in the so-called rendition programme.

There have been reports that an al-Qaida terrorist known as Hambali, who was suspected of involvement in the 2002 Bali bombing in which 202 people died, was taken to Diego Garcia to be interrogated following his capture in August 2003. A report in Time magazine quoted a regional intelligence official as saying he was being interrogated there two months after his detention.

An American detention facility of some sort is known to exist on Diego Garcia. In 1984 a review by the US government’s general accounting office of construction work on the atoll reported that a detention facility had been completed the previous December.

According to answers given to parliamentary questions, British military officials – who are nominally in command of the atoll – re-designated another building as a prison three months after the September 11 attacks.

In the past, Tony Blair, as prime minister, and Jack Straw, as foreign secretary, both denied the use of the atoll during the rendition programme, but these denials were contradicted by David Miliband, one of Straw’s successors, who told parliament in February 2008 that information had “just come to light” to show that two rendition flights stopped there to refuel.

That statement was made after human rights organisations obtained flight data showing that two aircraft closely involved in the CIA’s rendition programme had flown into and out of Diego Garcia.

A number of sources in the US have said there were a number of references to the CIA’s use of Diego Garcia in the report on the agency’s use of torture that was published last month by the US Senate intelligence committee.

Since then the UK Foreign Office has evaded a series of media inquiries about Diego Garcia and about the report, and has instead responded with a stock response.

Asked about Wilkerson’s comments, a spokesperson issued the same statement: “The US government has assured us that apart from the two cases in 2002 there have been 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.”

The Foreign Office has also performed a number of twists and turns when asked questions about the fate of flight and immigration records relating to Diego Garcia.

Last July the Foreign Office minister Mark Simmonds told Andrew Tyrie, the Tory MP who has been investigating the UK’s involvement in the rendition programme for almost a decade, that daily records were “incomplete” due to water damage.

The following day, however, a Foreign Office official was photographed in Whitehall carrying a batch of emails that showed that Scotland Yard detectives had taken possession of “monthly log showing flight details” and “daily records [obscured] month of alleged rendition”.

A few days later, Simmonds told MPs that “previously wet paper records have been dried out”, and that “no flight records have been lost as a result of the water damage”.

Two months after that, the Foreign Office told the Commons foreign affairs committee that a number of immigration records relating to civilians landing on Diego Garcia “have been damaged to the point of no longer being useful”.