Suspect 'M' last month became the first person to appeal successfully against being held without charge under the UK's new terrorism laws - after 15 months in Belmarsh prison.
The authorities defend conditions at Belmarsh
As the Home Office is angered by the release of another suspect, G, on bail, M told BBC Radio 4's Today programme about his experience.
He said: "I don't [know] why they arrest me and until now I didn't know why. Sometimes you feel you are like [an] animal inside the cage."
M, who cannot be named for legal reasons, said his experience - not knowing when he would be released - was psychologically damaging.
"That time it means for me that's my grave. That means you are going to stay in that prison until you die.
"You think that you are in prison and you have children [who] are being brought up without a father. And I was certain that the children without a dad, they would have a very disturbed future."
M was accompanied during the interview by successful human rights solicitor, Gareth Pearce, who often prompted him.
M said he saw similarities between the way he was held and the American detention camp, Guantanamo Bay. He was not able to see all of the evidence the British authorities said they had against him.
And a legal representative, appointed on his behalf, was not able to discuss it with him.
The government accused M of membership of the Libyan Islamic Fighting Group. It said he had been involved in the provision of false documentation and money to Islamist extremists.
M would not answer questions on these allegations, and his solicitor said to do so would give credibility to a process she said was outrageously unfair.
M criticised the Special Immigration Appeals Commission, known as Siac.
"This sort of court reminds me exactly what my country did with the detainees in Libya - exactly the same.
"I believe I'm [an] innocent man and I did nothing against this country."
M said after he was sent to Belmarsh, he was not questioned once.
"They did not question me once. If I am a suspect of terrorism, if they are thinking maybe I will do
something against this government or this country, why didn't they come to me to
ask me any questions?"
And he said the impact of imprisonment on the other detainees has been dramatic.
"I know some of them outside the prison, their behaviour and how they are. When I saw them inside the prison, they are completely different - their way of thinking and also physically - most of them they lost weight."
M said one prisoner had contemplated suicide.
"Three or four of them they have become mad - exactly mad. They are not controlled themselves - they are not thinking in [a] good way.
"They are talking like you feel they are crazy - exactly they are crazy. This law is not lawful - it is unlawful to detain people inside the prison indefinitely."
The Home Office says the prisoners are being treated well and that they have adequate access to mental health care.
They also note that the men are free to leave at any time as long as they leave the country, although M feared being killed if he returned home to Libya.