Babar Ahmad, who is accused of running a US-hosted website which encouraged terrorism, said he has never been formally questioned about the allegations against him or been presented with any evidence.
Mr Ahmad, speaking on the BBC Radio 4 World at One programme following a High Court challenge by the broadcaster to secure the interview, admitted he had previously fought “battles” in Bosnia but said he believed “terrorism to be wrong”.
He told the programme: “I am facing extradition to the United States and spending the rest of my life in solitary confinement.
“I have never been questioned about allegations against me and I have never been shown any evidence against me.
“It is fair to say I’m fighting for my life and I’m running out of time.”
Mr Ahmad said that if he had been charged and tried in 2003, he would likely have been released from a British prison by now, even if he had been found guilty.
He accused the British police of “outsourcing” the case to the Americans.
He said: “All the offences against me are alleged to have happened in this country.
“Had the police and CPS put me on trial in 2003 – which they could have done – I would have left prison years ago regardless of the outcome.
“I have been in this nightmare fighting extradition for the past eight years.
“I absolutely reject any allegation that I have supported terrorism and in any way and in any place – whether in Chechnya, or Afghanistan, or any other part of the world.
“I believe terrorism to be wrong and I believe targeting and killing innocent people to be wrong.”
And he added: “The right place for me to respond to these allegations is either in a court of law or a formal police interview.”
The BBC is scheduled to broadcast the full interview on Newsnight tonight.
Mr Ahmad said he faced spending the rest of his time in solitary confinement if he was handed over to the Americans and questioned whether anyone could prepare themselves for such a fate.
He said there was “no chance” his family would be able to come and visit him.
He said: “I’m going to a foreign land, where you don’t know anyone, where we have nothing to do with them, far away from your family and loved ones.
“It is a nightmare no one would wish on their worst enemy.
“I try not to think about it. The future is just too horrific to think about.”
The European Court of Human Rights is due to rule on Tuesday whether Mr Ahmad, and others including Abu Hamza, should face extradition to the US.
The court has been considering whether transfer to the US Penitentiary, Administrative Maximum, Florence, Colorado – known as a supermax prison – would breach Article 3 rights on prohibition of inhuman and degrading treatment.
The BBC carried out its Newsnight interview at HMP Long Lartin following a year-long battle with the Ministry of Justice for the right to broadcast and film an interview with Babar Ahmad.