Police investigating the mysterious death of an Egyptian billionaire accused of being a Mossad double agent cannot find a vital piece of evidence, The Times has learnt.

Shoes worn by Ashraf Marwan when he fell five floors from his apartment in Central London have disappeared and are feared to have been destroyed, police admitted.

The disclosure has angered Dr Marwan’s family and friends, who believe that the footwear held vital forensic evidence that could have established whether he was murdered.

Meanwhile The Times has been told that police are to interview a new witness who claims to have seen two men on the balcony of Dr Marwan’s apartment in the moments after he died.

The men, wearing suits and of Mediterranean appearance, were said to have peered over the balcony at his body before disappearing inside the flat.

Dr Marwan, 62, a businessman and son-in-law of the late President Nasser, and former political and security adviser to President Sadat, died on June 27 after falling from his suite of apartments in Carlton House Terrace.

His death came after recent allegations over his role during the 1973 Yom Kippur War. The former head of Israeli military intelligence had claimed that Dr Marwan was an Israeli spy. Others said that he was an Egyptian double agent, feeding Israel misinformation with the knowledge of the Egyptian Government.

Police have described his death as unexplained and are exploring three possibilities: that he was murdered, jumped or fell accidentally.

Dr Marwan’s body had been stripped but was sent to the mortuary still wearing a pair of shoes. They could have been vital evidence, because Dr Marwan would have had to have stepped on to a ledge or a plant pot to jump, family members said. But he suffered from a severe nerve condition affecting his feet, and could not step into the bath without assistance, they said.

For Dr Marwan to have jumped off the balcony, he would have had to step into a plant pot, and climb over an air-conditioning unit, a source said. If he had done so, material such as soil from the plant pots or paint would have been left on his shoes.

The new witness is believed to have been inside the Institute of Directors’ building at 116 Pall Mall, which backs on to Dr Marwan’s apartment.

The man, who was on the third floor, has claimed that he saw Dr Marwan fall past the window. He rushed over and looked up to see two men calmly looking down at Dr Marwan’s body from a balcony, a source said.

A source close to the investigation has also disclosed that Dr Marwan’s wife, Mona, has told police that her husband warned her three times that he might be murdered. His latest concerns came after an Israeli court ruled in early June that Major-General Eli Zeira, who headed Israeli Military Intelligence during the 1973 war, leaked Dr Marwan’s identity.

The Times disclosed two weeks ago that police have been told that the only known copy of Dr Marwan’s memoirs disappeared from his flat on the day of his death.

Israeli sources have claimed that Dr Marwan was recruited by Mossad in 1969 and in 1973 handed over files that showed Egypt’s plans to cross the Suez Canal. However, Egyptian sources have said Dr Marwan fed misinformation to the Israelis for years.

Dr Marwan moved to Britain after President Sadat’s assassination in 1981.

The Metropolitan Police acknowledged yesterday that his shoes had gone missing.

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