Detectives investigating the mysterious death in London of an Egyptian billionaire who had been accused of being an Israeli secret agent are examining claims that an explosive account of his life disappeared from his flat on the day that he died.

The Times has learnt that the only known copy of a book written by Ashraf Marwan vanished when he fell four floors to his death from his apartment in St James’s Park.

The disclosure came as Dr Marwan’s son spoke for the first time of his family’s belief that his father was murdered. His claims will increase speculation that another former foreign agent may have been murdered on British soil after the poisoning last year of Alexander Litvinenko, the former KGB agent.

Dr Marwan, 62, a businessman and son-in-law of the late President Nasser, died at about 1pm on June 27 after falling from a window at his suite of apartments in Carlton House Terrace. His death followed allegations over his role during the 1973 Yom Kippur War. Some authors have claimed that he was a well-connected Israeli spy. Others have said that he was an Egyptian double agent, feeding Israel disinformation with the knowledge of the Egyptian Government.

Until now police have described his death as unexplained and explored three possibilities: that he was murdered, that he jumped or that he accidentally fell.

Sources have told The Times, however, that police have been advised that the only known copy of Dr Marwan’s memoirs disappeared from his flat on the day of his death.

Three volumes of the book, each about 200 pages, were taken as well as the tapes on to which they had been dictated. A source said that on the day he died, Dr Marwan was due to fly to the United States to finalise the last chapter.

The book was expected to be released in October on the anniversary of the Yom Kippur War, the source said. It gave an insider’s account of the Middle East between 1969 and 1978, using documents that had been officially declassified by the US and Britain. His account rejected claims that he was an Israeli spy.

A team of detectives has now been asked to interview a number of witnesses, including the concierge to his apartment building, neighbours and a number of family members.

Dr Marwan’s eldest son, Gamal Marwan, 40, said that he and the family were convinced that his father had been murdered. “There is no way that my father killed himself. He was a soldier, and died as a soldier, and he died serving his country. I believe that he was murdered and I have told the authorities so,” he said.

Some commentators have claimed that Dr Marwan may have taken his own life after undergoing three serious heart operations that had made him prone to depression. However, those close to him say that there is no evidence that he did so.

When he had previously undergone life-threatening heart surgery, Dr Marwan had closed down his open positions in the global stock market and converted his capital into cash, a source said. On the day that he died, he had not done so.

Friends of Dr Marwan claim that he had booked a series of long-term engagements in the weeks before his death. He had organised wedding anniversary celebrations for July 7 in Spain and was planning to attend a Buckingham Palace garden party in early July and had invited eight friends. He had also planned to make a pilgrimage to Mecca in December.

Those close to Dr Marwan believe that he could not have fallen accidentally. They have identified one balcony and one window in his bedroom through which he must have left the building. The balcony rail is 1.4m (4½ft) high while the window is 1.6m off the floor.

Dr Marwan suffered from leg and foot problems and so could not even step into a bath unaided, one source said. “He walked with a cane. He was not Michael Jordan, and could not have jumped that high, and did not use any visible means to jump out.”

At least four of Dr Marwan’s family members have been interviewed by detectives, who are trying to identify a number of visitors to his apartment complex on the day that he died.

There was only one other person, a maid, who was known to be inside the seven-bedroom apartment that day. Reports have claimed that she was not aware there was anyone else in the building at the time of his death.

Police have examined CCTV footage, but there are few cameras trained on the apartment block. There are five entrances to the building and police have also examined a damaged aerial on the wall of the building.

Dr Marwan met his wife, Gamel Nasser’s daughter Mona, at university. He became a close confidant of Nasser and later became political and security adviser to President Sadat.

Israeli sources have since claimed that he was recruited by Mossad, the Israeli intelligence agency, in 1969 and in 1973 handed over files that showed Egypt’s plans to cross the Suez Canal. However, Egyptian sources have said that Dr Marwan fed disinformation for years to the Israelis with the blessing of the Government. Dr Marwan was hailed as a national hero by Sadat’s successor, President Mubarak. He moved to London 25 years ago.

The Westminster Coroner will hold a meeting on September 4 to set a new date for Dr Marwan’s inquest.

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