Letters written by former South African president Nelson Mandela during his 27 years in jail reveal the agony of being separated from his family. Excerpts of the letters, which go on sale on Tuesday, show his frustration as his wife and children are harassed by the apartheid government. "I feel I have been soaked in gall," he told Winnie Mandela as she served 18 months in solitary confinement. In a letter to his children he wrote: "For long you may live like orphans." Many of the letters were copied by Mr Mandela into exercise books which were confiscated by the authorities. They were finally handed back to him by a former security policeman in 2004. The private correspondence reveals a husband and father, struggling to keep his family together while under considerable political and emotional pressure. In June 1969, he wrote to his two daughters, Zeni and Zindzi aged 9 and 10 respectively, when both he and their mother were in prison. "Now you will get no birthday or Christmas parties, no presents or new dresses no shoes or toys," he told them. That same year, he was not allowed to attend the funeral of Thembi, the elder of two sons from his first marriage, who died in a car crash aged 24. "When I was first advised of my son's death I was shaken from top to bottom," he wrote. A letter to Winnie Mandela in August 1970 shows his anger at his family's plight. "I feel I have been soaked in gall, every part of me, my flesh, bloodstream, bone and soul, so bitter am I to be completely powerless to help you in the rough and fierce ordeals you are going through," he wrote. Fraught relationship The letters also document the path of his relationship with Winnie Mandela. In 1976 he wrote that his main problem was "my sleeping without you next to me and my waking up without you close to me, the passing of the day without my having seen you." At the time, she was promoted actively by the African National Congress as a symbol of its struggle against apartheid. But by the mid-1980s her actions were becoming increasingly controversial and their relationship appeared to have become fraught. In 1987, he wrote to a friend about Winnie Mandela's furious response when he told her how well their two daughters had grown up: "She reminded me: 'I, not you, brought up these children whom you now prefer to me.' I was simply stunned." Although she walked by his side when he was released in 1990, they separated in 1992 and divorced four years later. Passages from the letters have appeared in the British newspaper, The Sunday Times, and in papers in South Africa. They are being published in a book, Conversations with Myself, which incorporates an archive of diaries and private recordings as well as letters. In one excerpt from the book, it is clear that Mr Mandela had become wary of his growing international reputation while being held in jail on Robben Island. "One issue that deeply worried me in prison was the false image I unwittingly projected to the outside world; of being regarded as a saint. "I never was one, even on the basis of the earthly definition of a saint as a sinner who keeps trying," he wrote. Credit: BBC