Scotland Yard detectives are planning to travel to Guantanamo Bay to interview prisoners as part of an inquiry into an MI6 officer, it has been reported.
The force is attempting to track down prisoners who were at the Bagram air base in Afghanistan in January 2002, ITV News said.
The move is said to be part of an investigation into claims the MI6 officer witnessed the alleged inhumane treatment of detainees by the US military.
He is reported to have spoken to officials in London in 2002, raising concerns about the way a detainee had allegedly been treated by the US military.
ITV News said the MI6 officer was told not to intervene, but to raise the issue with a senior US official. It has been reported that he took no further action.
It is not alleged that the MI6 officer was involved in any alleged mistreatment himself.
A Scotland Yard spokesman would not confirm whether its detectives were planning to interview Guantanamo Bay prisoners. He said: "We are not giving a running commentary on this investigation."
US government permission would be needed for the interviews to go ahead.