Miriam Margolyes has defended her controversial decision to reveal what she believes is the truth about the early death of the great British cellist Jacqueline du Pré. In her new memoir the actor claims that a mutual friend was responsible for secretly assisting the suicide of 42-year-old Du Pré, who was suffering the serious effects of multiple sclerosis. It is, Margolyes argues, now her duty to speak out, three decades on, although she knows some readers will question her right to tell such a private story. “I’m not sure I can answer that. But I felt it was such an important story about a very great artist, it should be known, a kind of public duty,” Margolyes explained in a recent interview for an upcoming issue of the Observer Magazine. The veteran actor, 80, who is perhaps best known today for playing Professor Sprout in the Harry Potter films, said she made “a deliberate decision” to include the allegation and that she wonders if others will come forward to back her up. Margolyes has a long reputation as an uncompromising plain-speaker and her book, This Much is True, is filled with naughty anecdotes and ribald stories. However, this particular astonishing reminiscence has upset members of Du Pré’s family, including her former husband, the pianist and conductor Daniel Barenboim. Speaking to the Daily Mail, Barenboim has referred to Margolyes’ account as “unverifiable”, adding it has “absolutely nothing to do with the reality of Jackie’s passing”. In her memoir Margoyles recalls that her London therapist, Margaret Branch, who died in 1997, once confided that Du Pré had invited her to her Kensington home in 1987 to help put an end to her life. Branch, who had trained as a nurse, reportedly told Margolyes she arrived with a syringe and a lethal drug and carried out the wishes of the celebrated classical musician. Branch then asked Margolyes to keep the secret until after her death. “I felt it was wrong to say it then. And this time, I thought, it’s an important story. I think it’s wonderful. Heroic, actually,” said Margolyes, adding that she continued the friendship with Branch after her period of therapy. “I don’t know if she told anyone else … I think that I am the sort of person that people tell things to.” Oxford-born Du Pré, who played on two Stradivarius cellos, became a household name during the 1970s and is still regarded as one of the finest classical musicians of modern times. Her complicated personal life, and her marriage to Barenboim, who is now music director at the Berlin State Opera, has been a source of public fascination, as well as the inspiration for biographers and dramatists, partly in the light of her final tragic struggle with illness. She first felt symptoms of MS in her fingers at the age of 26. Margolyes’ account suggests Branch acted believing “it was the highest mark of love for Jacqueline that she could show, to release her from the horrors of her illness” and that she sought reassurance from the cellist at the last that she still wanted to die. But one of Du Pré’s surviving companions, Cynthia Friend, 81, told the Daily Mail that she does not credit the story. “I don’t believe it for one minute,” she said. At the end, Friend testifies, Du Pré was too ill to speak or hold her head up properly and was never left alone by her nurse or other friends. “I cannot imagine what Jackie would say, if she heard these things,” she said. Du Pré’s death certificate shows the cause of death as “bronchopneumonia and multiple sclerosis”. Margolyes told the Observer that her publishers, John Murray, were unsure whether to include the incident: “But it was an amazing story that she told. Do you think people are going to pick it up in the newspapers or something?”