In his autobiography Olaudah Equiano, a former slave who bought his freedom and then became a leading voice in the movement to abolish slavery, claimed he was born in Essaka, Igboland in what is now southeastern Nigeria in 1745. Equiano (who also went by the name Gustava Vassa) described how he was taken by slave traders and shipped to the Caribbean. It was the first written account by an African in English of the slave journey.

But in a book to be published next month, University of Maryland professor Vincent Carretta claims there is more evidence to suggest that Mr Equiano was born in South Carolina and concocted the tale of the slave journey from other people's accounts.

Mr Carretta, a world authority on Equiano's life, has unearthed a baptismal record from 1759 and a 1773 ship's muster both of which list South Carolina as Equiano's birthplace.

"It's not a smoking gun but it is strong circumstantial evidence," he says, insisting that there are no doubts about the authenticity of the rest of Equiano's accounts. "If you read the first three chapters they read like anthropology. The rest reads like autobiography. Once he enters history he is amazingly accurate."

Mr Carretta's findings have divided academics on both sides of the Atlantic. The atmosphere at a conference at Kingston University in 2003 became "a tad overwrought" as he presented them.

"They asked me why I was doing this to Equiano. I said: 'You can question my motives all you want. Equiano's my hero. I'm crazy about him. But even if I wasn't the data are still there'."

Professor Paul Lovejoy of York university in Toronto argues that the overwhelming body of evidence suggests Equiano was born in Africa and that his whole life story should not be distorted to account for two documents of debatable veracity. "The thing that doesn't fit is the document that says he was born in South Carolina," says Mr. Lovejoy. "Everything else fits. The one thing that's odd - that's the one that has to be questioned, not the other way around."

Equiano's significance to transatlantic history has grown precipitously over the last few decades. History professor James Walvin bought a first edition of his book in 1967 for 5 shillings; today it is worth $12,000.

"So many people have a stake in Equiano that it is bound to upset a lot of people," says Prof Walvin, from York university in England. "These are two documents among many. You can't ignore them. But if it's true then it's a dynamite issue."

Others, like Paul Gilroy, of the London School of Economics, believe the dispute has been overblown. "Does the issue of Olaudah's birthplace undermine the ... historical meaning of catastrophic mass death?" asks Professor Gilroy.

Equiano's descriptions of the journey are graphic. "The closeness of the place and the heat of the climate added to the number in the ship, which was so crowded that each had scarcely room to turn himself, almost suffocated us," he writes in The Interesting Narrative of the Life of Olaudah Equiano, or Gustavus Vassa, the African, Written by Himself. "The shrieks of the women, and the groans of the dying, rendered the whole a scene of horror almost inconceivable."

Mr Carretta says Equiano may have fabricated the accounts for reasons of political expediency. "The priority for abolitionist cause at the time was abolishing the slave trade rather than slavery. If he had said he was born in South Carolina he would have been much less useful. There was a need for the voice. He was aware of the need and in a position to give his voice."