Linda Grant, who on Wednesday won the Orange prize for her novel When I Lived in Modern Times, last night rejected allegations that she plagiarised the work of an American academic.
"What should have been the happiest day of my life has been completely destroyed," she said last night. "Instead of celebrating, I spent it literally with my stomach lurching."
Her novel, about a young London woman who becomes enmeshed in Zionist politics in Tel Aviv in the aftermath of the second world war, confounded the bookmakers on Tuesday night, beating the favourite, Zadie Smith's White Teeth, to take the £30,000 prize. Ms Grant's novel was the unanimous choice of the judges.
Within hours of her success anonymous faxes were circulating to individuals and at least one national newspaper, alleging that Ms Grant, who is also a Guardian journalist, had stolen the work of American academic and author A J Sherman, by quoting verbatim chunks of his book Mandate Days, British Lives in Palestine 1918-1948, and would be sued for plagiarism.
Her agent, Derek Johns, said: "This looks like harassment, after Linda winning the big prize. The anonymity makes it all the more reprehensible."
In fact the paperback edition of When I Lived in Modern Times is printed with a prominently displayed, acknowledgement of Sherman's work, agreed after weeks of discussions between his publishers, Thames and Hudson, and Ms Grant's publishers, Granta. The acknowledgment reads: "I am greatly indebted to A J Sherman's invaluable research on this period. Some of the dialogue given to my colonial characters has come directly from letters, memoirs and diaries, from which he quotes."
Ms Grant said last night: "I used the sentences - never whole chunks - only as quotes from material he himself was quoting, to give colour and character to the dialogue. I never used a single original word of A J Sherman's, and I estimate that what I used amounted in total to about 0.04 per cent of the entire book."
She explained that her original text contained two and a half pages of acknowledgements of her many sources, including the Sherman book, and others, and taped conversations and interviews. After much discussion Granta decided that this scale of acknowledgement was uneccessary, since the book was fiction.
However, she did acknowledge Mandate Days in a piece she wrote for the Guardian Weekend, about the novel and her research for it. She subsequently received "a friendly letter" from A J Sherman, she said, saying he had read her book and enjoyed it, but had recognised the quotes from his own work and felt it should be acknowledged.
"I said yes, right, absolutely, and explained what I had originally done."
Protracted and detailed exchanges followed between the two publishers to agree the exact form of the acknowledgement, which will be included in all subsequent editions.
"I thought it was all done, finished, settled. I felt sick when it kept coming back. There was never any threat to sue, because there was never anything to sue about.
"I feel that this is now malicious harassment of me, and I cannot understand it."
It was not possible to contact a representative of Thames and Hudson last night.
Ms Grant was a surprise choice for the award. Many thought Zadie Smith's bravura survey of multicultural London, White Teeth, was a dead cert to take the title. But she had stirred controversy by references to the Tory leader William Hague's attacks on asylum seekers.
More on the Orange prize shortlisted books on the Guardian network at www.booksunlimited.co.uk