The book, passages of which were published in newspaper Libération on Wednesday morning under the headline "The Bettencourt affair arrives at the Elysée", re-ignites an issue which first became public in June 2010.
The affair revolved around allegations from a former Bettencourt employee that Nicolas Sarkozy's UMP party had received illegal funding from the billionaire as part of his presidential election campaign. These allegations were denied by the party.
The Elysée Palace, official residence of the president, was quick to deny the new allegations.
"These are scandalous, unfounded and untrue allegations," a spokesman told Reuters.
The charges are made in a book, 'Sarko m'a tuer' (Sarkozy killed me), written by two journalists from Le Monde newspaper.
They quote a judge who previously worked on the inquiry, Isabelle Prévost-Desprez, who said she was surprised by the fear that many witnesses had when they were being questioned.
"[They were] scared to make a statement about Nicolas Sarkozy," she said.
Prévost-Desprez, who is no longer part of the official inquiry, claims that Bettencourt's nurse spoke to her clerk after the judge had interviewed her and said she had seen "money being handed to Sarkozy" but that she "couldn't say it in my statement."
Government spokeswoman and budget minister Valérie Pécresse criticized the "press rumours" on television channel France 2 on Wednesday morning.
"When there are accusations to be made, they shouldn't be made in a book or in the press but in court," she said.