The death of Marwan, suspected of being a double agent for Israel during the 1973 war, comes amid a controversy in Egypt about his role in the intelligence and business worlds.
The Middle East News Agency said initial indications suggested Marwan fell from his apartment balcony in the St. James Park neighborhood in London. MENA said Scotland Yard was investigating.
Some opposition lawmakers recently demanded an investigation after Egyptian papers carried reports from Israeli media about Marwan's possible role as a double agent during the 1973 war, when Egypt and Syria waged a sneak attack against Israel on the Jewish holy day of Yom Kippur.
The Egyptian government has never commented on these allegations. MENA reported that Marwan received the highest honors for his "achievements" during the 1973 war from former President Anwar Sadat. The news agency did not elaborate.
Maj. Gen Eli Zeira, who was fired from his position as head of military intelligence over Israel's failure to predict the 1973 Arab attack, said in a 1993 book that Israel was caught by surprise because it was led astray by a double agent he did not identify. But Marwan's name subsequently was released to the press.
The head of Israel's Mossad spy agency at the time of the war, Zvi Zamir, accused Zeira in 2004 of leaking the agent's name to journalists in an attempt to explain his own failures. Zamir compared Zeira to Mordechai Vanunu, who spent 18 years in prison after betraying information about Israel's nuclear weapons program.
Zeira hit back by suing Zamir for libel. But the case ended just last month when a court confirmed Zeira leaked Marwan's identity.
According to the Israeli media reports, Marwan first walked into the Israeli Embassy in London in 1969 and volunteered to give information but was turned down. He later was allegedly recruited by the Israeli intelligence agency, Mossad.
Born to a father who was a military officer in Nasser's presidential guard, Marwan joined the army himself after he finishing a degree in chemical engineering. He later worked as an assistant to Nasser and after Nasser's death in 1970, he became a political and security adviser to Sadat.
In the 1970s, Marwan worked as head of Egypt's huge government-owned military industry complex before he retired and moved to Britain 25 years ago to work in business.