Nelson Mandela used the trial to attack the state

He was released in 1990, and four years later became president after South Africa's first democratic multi-racial elections.

The newly-released recordings offer a fascinating insight into a remarkable moment in the country's history.

In his autobiography, Mr Mandela tells how he had decided to use the trial not to obtain his own acquittal, but to put the apartheid state on trial.

'Phenomenal moment'

He told the judges that he was prepared to die for the ideal of a democratic and free South Africa.

The judge didn't know what to say

Denis Goldberg

Co-defendant Denis Goldberg sat two seats away from Nelson Mandela as he spoke.

"It was an absolutely phenomenal moment... because in effect he was challenging the apartheid judge to hang all of us," he said.

"I don't remember any fear. I just remember a sense of tremendous pride.

"I remember weeping at the sheer dignity with which Nelson Mandela delivered those words.

"And then a terrible, tense silence. Even the judge didn't know what to say and then there was a kind of collective sigh as the tension relaxed."

CD recording

The British Library owns one of the few remaining dictabelts, and it has now transferred Mr Mandela's words to a CD.

Dr Rob Perks, curator of oral history at the British Library, said: "What amazed us, given the age and fragility of these dictabelts, is just how good the sound quality is."

Mr Mandela's words at the trial were transcribed and reported the world over, but this is the first time that anyone who was not in the courtroom 37 years ago has heard them spoken by the man himself.

"There's something about being able to hear the pauses, the intonation, the way in which his voice changes at different parts of the trial, that really gives us a lot of new information about Mandela and his state of mind at the time," said Mr Perks.