Scotland Yard is to look into allegations that British officials were complicit in the torture of a prisoner at Guantanamo Bay, ITV News has learnt.
It could lead British detectives to ask for US government permission to interview Shaker Aamer at Guantanamo Bay.
His case is one of three that are to be considered by Metropolitan Police detectives. The investigations are understood to include claims against MI6 and MI5 officers.
The decision was made by a joint Crown Prosecution Service and Metropolitan Police panel.
Earlier this year the panel decided detectives should investigate claims of British involvement in the ill treatment of two Libyan men and their families.
But Mr Aamer is the last remaining British national held at Guantanamo Bay.
It is claimed he has been subjected to torture including sleep deprivation, noise torture, stress positions and other forms of mistreatment.
The allegation is that British officials visited him, or asked questions, while aware that he was being tortured.
Mr Aamer is a Saudi Arabian citizen but is a legal permanent resident of the UK. He is married to a British woman with four children living in London.
He was arrested in Afghanistan in 2001 and taken to Guantanamo; he has never been put on trial there. He has long been cleared for release, according to the charity Reprieve.
His US lawyer Cori Crider said today: "This is a positive development. What has happened to Shaker was appalling and we look forward to co-operating with the police."
In a statement today the Crown Prosecution Service said:
On 12th January 2012 the DPP announced that a joint CPS and MPS [Metropolitan Police] Scoping Panel would convene to assess a number of allegations of complicity to torture made against British Officials.
The panel has now had the opportunity to sit and, having assessed twelve cases, it has referred three to the MPS to consider further investigation.
The MPS has decided to undertake further investigation into these three cases.
Legal representatives for those making the allegations are aware of the panel's assessments and officers from the MPS are seeking, where possible, to meet with those that have made allegations in order to explain the individual decisions.