Peter Moore is said to be in "remarkably good" health
Freed hostage Peter Moore, 36, is being debriefed at a secret location by the Met Police, the BBC understands.
The IT expert from Lincoln's account of his capture in Iraq in 2007 is likely to be crucial to inquiries into the murder of three of his bodyguards.
The bodies of Alec MacLachlan, 30, of Llanelli, Jason Swindlehurst, 38, of Lancs, and Jason Creswell, 39, of Glasgow were handed over last year.
A fourth guard, Alan McMenemy, 34, from Glasgow, is also believed to be dead.
The Foreign Office believes his body will also be handed to UK authorities soon.
BBC security correspondent Frank Gardner said Mr Moore was said to be in "remarkable shape, both physically and mentally".
"Slowly and painstakingly, he's giving police detectives and psychiatrists as accurate an account as he can of what happened to him and his four bodyguards from the moment they were kidnapped in Baghdad," he said.
Separated from guards
They were taken from outside Iraq's finance ministry in May 2007 by up to 40 men in police uniforms.
The kidnappers were understood to belong to an obscure militia known as the Islamic Shia Resistance, which demanded the release of up to nine of its associates held in US military custody since early 2007.
Several were handed to the Iraqi government, which later freed some as part of its political reconciliation process.
Qais al-Khazali, the leader of Asaib al-Haq - or the League of Righteousness - was transferred from US to Iraqi custody shortly before the release of Mr Moore on 30 December.
However, the Foreign Office insisted he was not released under any prisoner exchange scheme.
Mr Moore was separated from the others during the latter part of his captivity and was initially unaware they had been murdered.