"I didn't feel like I was free. Even now I don't feel that I'm free," he said.
"It's been seven years of literal darkness that I have been through. Coming back to life is taking me some time."
He added: "I don't have the regular person's feelings that people have. The feelings of happiness and sadness, I still don't have them.
"As far as I am concerned, nothing matters."
The former terror suspect said that the six years and 10 months he spent in detention had left him feeling "dead".
Later detained in Pakistan, Mr Mohamed said, he was interviewed for three hours by an MI5 officer calling himself John whose role, according to Mr Mohamed, was to support the American interrogators.
"If it wasn't for the British involvement right at the beginning of the interrogations in Pakistan, and suggestions that were made by MI5 to the Americans of how to get me to respond, I don't think I would have gone to Morocco," he said.
"It was that initial help that MI5 gave to America that led me through the seven years of what I went through."
The MI5 agent who questioned him has previously denied at the British High Court any suggestion that he threatened or put any pressure on Mr Mohamed.
Mr Mohamed said he had originally travelled to the region after becoming a practising Muslim, visiting Afghanistan because he had been told it "was where the real Islam was".
"There was just a word out there that Afghanistan was the real Islamic state at that time, and I should make my way over there," he said.
During the interview, Mr Mohamed's lawyer prevented him from answering questions about travel documents he had used to get to Afghanistan and a training camp he attended.
This was because Mr Mohamed's immigration status is currently under review.
Mr Mohamed said that in July 2002 he was flown to a secret site in Morocco where, he claimed, he was tortured by local officers asking him questions supplied by British intelligence operatives and showing him hundreds of photographs of Muslim men living in the UK.
"The interrogator who was showing me the file would say, 'This is the British file and this is the American file.'"
In the 'dark prison' I was ... dead. I didn't exist. I wasn't there. There was no day, there was no night
Mr Mohamed said that 70% of questions put to him had to have come from sources in the UK.
In the UK, the attorney general is continuing a review into whether to ask police to investigate allegations of British collusion in mistreatment of Mr Mohamed.
His lawyers have previously placed on record claims that the torture included a razor being used to slash his genitals.
In the interview, extracts of which were broadcast on Radio 4's Today programme, the former detainee told the BBC he had never been involved in any plots and had not attended terrorist training camps before 9/11.
Asked if he had been an al-Qaeda operative, he replied: "I don't even know what that means because how am I supposed to be an al-Qaeda operative?
"How do you become an al-Qaeda operative?"
In January 2004, Mr Mohamed said he was taken to a place he calls the "dark prison" in the Afghan capital, Kabul, where he said he almost lost his mind.
He claimed he was put in a dark cell with just a blanket on the floor.
Speakers attached to the walls pumped out music by the American rapper Eminem 24 hours a day for a month.
"In the 'dark prison' I was literally dead. I didn't exist. I wasn't there. There was no day, there was no night."
Following his experiences in Kabul, Mr Mohamed signed a confession which he said he agreed to only because he was told he would be flown back to the "dark prison" if he didn't co-operate.
Shortly after this he was sent to Guantanamo Bay where, he said, guards attacked him for refusing to give his fingerprints.
He claimed abuses at the camp had increased since President Barack Obama announced his intention to close it within a year.
Liberal Democrat foreign affairs spokesman Edward Davey said that Mr Mohamed's allegations "could not be more compelling".
William Hague, the shadow foreign secretary, said the UK's "name and reputation will be dragged through the mud" unless a judicial inquiry is held into the affair.
The director of human rights group Liberty, Shami Chakribarti, echoed calls for a full investigation, insisting that there could not be "one law for the government and another for everyone else".
On Thursday, a Home Office spokesperson said: "The government unreservedly condemns the use of torture as a matter of fundamental principle and works hard with its international partners to eradicate this abhorrent practice worldwide.
"The security and intelligence agencies do not participate in, solicit, encourage or condone the use of torture or inhumane or degrading treatment."
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