Shaker Aamer
Shaker Aamer was cleared for release by both the Bush administration in 2007, and again by the Obama administration in 2009. Reprieve

The last remaining British prisoner in Guantanamo Bay could be handed over to Saudi Arabia to prevent him revealing details of alleged torture, MPs have heard.

Shaker Aamer, 46, is said to have "seen too much" in the controversial detention camp, where he has been incarcerated for 13 years without charge, despite being cleared for release by both the Bush and Obama administrations.

During a House of Commons debate, MPs urged the release of Aamer who is reported to be suffering from post-traumatic stress disorder (PSTD), amid claims the US is in talks to hand him over to Saudi Arabia.

According to documents obtained by Freedom of information requests by Amnesty International, the US and Saudi Arabia have spoken several times about Aamer's case, including once in 2010 when the US instructed its Saudi embassy on "engaging Saudi Arabia on Shaker Aamer".

During the parliamentary debate, MPs discussed "deeply damaging" allegations that Aamer is still being held because he has witnessed an array of human rights abuses conducted by US authorities inside the detention camp.

During the debate, former shadow home secretary David Davies outlined the possible reasons why Aamer is still being held captive, including concerns he "had seen too much" and would be a threat to the US if released.

"If it is that he will embarrass them then that is again a doubling up of the guilt on their part," he said.

"Because frankly this is going to come out into the open at some point."

Labour MP John McDonnell added Aamer's case is one of the "worst cases of a miscarriage of justice in the last three decades".

He said "Shaker's release has now become urgent. As a result of more than a decade of detention and barbaric treatment, including extensive torture, his health has deteriorated significantly.

He added: "Why is Shaker still being detained? Why can he not be allowed to come home to his family? We can only speculate. Is it because he knows too much about what happened in Guantanamo Bay and will ensure that the truth comes out if he is released? it because he can bear witness to the involvement of not just United States but, possibly, British intelligence in the illegal, criminal torture that went on in Bagram, Kandahar and Guantanamo?"

Foreign and Commonwealth office minister Tobias Ellwood said: "The UK Government is committed to bringing Mr Aamer back to the UK and we have made our position very very clear to the US Government. We want him released as a matter of urgency and we know that they fully understand this request."

The Saudi-born national, who moved to the UK in 1996 and is now father of four British children, was captured by Afghan Northern Alliance forces in 2001 and handed to the US. He denies claims he was an associate of Osama Bin Laden, claiming he was in Afghanistan to conduct charity work.

Cori Crider, a director at human rights organisation Reprieve and a lawyer for Aamer, said: "It is a scandal that Shaker Aamer continues to languish in Guantanamo. Bland reassurances that the Obama administration is prioritising his case are no longer enough.

"We need a concrete timetable for his return home, and we must see answers on why this didn't happen years ago. For a start, we need to know what happened in secret meetings between the UK and US, and the US and Saudi Arabia – are these indications of an attempt to silence him by handing him over to the Saudi regime?"