Former US President George Bush kept prisoners in Guantanamo Bay despite knowing they were innocent to avoid political embarrassment and further the case for the war on terror, the former Chief of Staff to US Secretary of State Colin Powell has alleged.

Lawyers acting for Shaker Aamer - a father or four from Battersea who is the last British resident to be held in the Cuban prison camp - said the Colonel’s revelations furthered claims Mr Aamer was innocent, and added weight to claims he was tortured in Afghanistan.

In a sworn statement Colonel Lawrence Wilkerson, who retired in 2007 and has been a critic of the Bush administration, also said former Secretary of Defence Donald Rumsfeld and former Vice President Dick Cheney helped “indefinitely detain the innocent for political reasons”.

Colonel Wilkerson made a series of admissions in an affidavit in support of former Guantanamo detainee Adel Hassan Hamad, 52, a Sudanese worker released in 2007 after five year’s detention.

Mr Hamad claims, as does Mr Aamer, he was mistreated at Bagram, Afghanistan - including beatings, stress positions and being given little food - and is suing the US Government for ongoing physical and emotional problems and compensation for loss of wages and reputation.

The Colonel, who was Chief of Staff from 2002 to 2005, said Mr Cheney’s position on Guantanamo “could be summed up as ‘the end justifies the means’” and that he “had absolutely no concern that the vast majority of Guantanamo detainees were innocent or that there was a lack of any useable evidence for the great majority of them”.

The Colonel said President Bush “was involved in all of the Guantanamo decision making” and Cheney “ran circles around Bush” by appealing to his “cowboy instincts”.

In the statement he said: “Their view [of Cheney, Rumsfeld and others] was that innocent people languishing in Guantanamo for years was justified by the broader war on terror and the capture of the small number of terrorists who were responsible for the September 11 attacks, or other acts of terrorism.

"Moreover, their detention was deemed acceptable if it led to a more complete and satisfactory intelligence picture with regard to Iraq, thus justifying the administration’s plans for war with that county.”

He went on to explain it was “politically impossible” to release prisoners because the Department of Defence would be left without a plausible explanation if the detainee took up war with the US “whether the released detainee was subsequently found to be innocent by the receiving country, or whether the detainee was truly a terrorist”.

He said the administration were also concerned detainees would lift the lid on conditions at Guantanamo and how the US caught “combatants” after it invaded Afghanistan.

He said Hamad was one of the “victims of incompetent battlefield vetting”.

He said: “It became apparent to me as early as August 2002, and probably earlier to other State Department personnel who were focused on these issues, that many of the prisoners detained at Guantanamo had been taken into custody without regard to whether they were truly enemy combatants, or in fact whether many of them were enemies at all.”

Wilkerson noted many detainees - including Shaker Aamer - were handed over to the US by bounty hunters who were promised as much as 150 million Afghanis (about $5,000, more than five times the per capita annual income in Afghanistan) after the Afghan invasion for handing over al-Qaeda suspects to the United States.

“Such practices meant that the likelihood was high that some of the Guantanamo detainees had been turned in to US forces in order to settle local scores, for tribal reasons, or just as a method of making money,” he said.

Because most detainees were turned over by bounty hunters or foreign governments it was the case, he said, “that often absolutely no evidence relating to the detainee was turned over, so there was no real method of knowing why the prisoner had been detained in the first place”.

He admitted: “By late August 2002, I found that of the initial 742 detainees that had arrived at Guantanamo, the majority of them had never seen a US soldier in the process of their initial detention and their captivity had not been subjected to any meaningful review.”

Mr Aamer, who has now been held in Guantanamo for more than eight years despite never being charged with any offence, alleges British secret service agents were present at his torture at Bagram, Afghanistan.

In the statement Colonel Wilkerson said: “The claims made by Mr Hamad are consistent with information about other abuses that occurred in Bagram.”

Brent Mickum, who represents Shaker Aamer in the US, said the Colonel’s statement would help his client, who he believes is partly being held because of events he witnessded in Guantanamo.

Mr Mickum said: “It helps. This again confirms what we have been saying. That detainees like Shaker Aamer are being held because of what they know.”

Making the statement, which was filled in the district court for the district of Columbia, Colonel Wilkerson said: “I have made a personal choice to come forward and discuss the abuses that occurred because knowledge that I served an administration that tortured and abused those it detained at the facilities in Guantanamo Bay and elsewhere and indefinitely detained the innocent for political reasons has marked a low point in my professional career and I wish to make the record clear on what occurred.

"I am also extremely concerned that the Armed Forces of the United States, where I spent 31 years of my professional life, were deeply involved in these tragic mistakes.”