Prosecutors had called the model to testify at the court in The Hague, the Netherlands, in the hope that she could provide evidence that Taylor had handled diamonds allegedly used to purchase weapons during the 1991-2001 Sierra Leone civil war.
Taylor is on trial on charges of murder, rape, mutilation, sexual slavery and conscription of child soldiers during wars in Liberia and Sierra Leone, in which more than 250,000 people were killed.
Campbell told the court that she received a pouch with a number of "dirty-looking stones" after attending a dinner hosted by Nelson Mandela in South Africa in 1997, at which Taylor was also a guest.
But Campbell said she did not know who the gift was from, and handed them over to Ratcliffe the following day.
Ratcliffe confirmed Campbell's account, saying he received them on September 26, 1997.
Campbell had wanted the fund to use them, but Ratcliffe said he did not want to involve the charity in any possible illegal activities.
"In the end I decided I should just keep them," said Ratcliffe, but added that he recently handed them over to South African authorities.
Ractliffe, who is now a trustee of the charity, told The Associated Press news agency on Friday that he will be a witness at the international war crimes court in the trial of the former Liberian president.
South African police confirmed that Ratcliffe had given a number of stones to authorities.
"They were handed over to the police and now they have been sent to the diamond board for authentication," Musa Zondi, a spokesman for the special investigations unit of the South African police, told the AFP news agency.
"Obviously there has to be an investigation, but first we have to wait and get the diamonds authenticated before we can say anything."
The British model told the court on Thursday that she was woken in the middle of the night by two men at her door who offered her a pouch containing the stones, as a gift.
Campbell, who said the men did not say who the gift was from, told Carol White, her then modelling agent, and Mia Farrow, a US actress, about the pouch the following morning.
According to Campbell, either Farrow or White said the rocks must be diamonds and were probably a gift from Taylor.
The prosecution says White had heard Taylor say he was going to give Campbell a diamond during the dinner, and that she was there when the model received it.
Campbell insisted she was alone when the two men came to her door.
White and Farrow, who both attended the dinner, are due to testify about the gift at the war crimes court on Monday.