The book - 'What Happened to Netaji?' - by former journalist Anuj Dhar details three prominent theories of Bose's death before zeroing in on what has come to be known as the Faizabad angle to the Bose mystery.
"A source with a direct access to a highest-level contact in the government told me, strictly on the condition of anonymity, that the Prime Minister of India had in his possession an ultra secret file which held the key to unravelling the Bose mystery," Dhar said.
"Emissaries, including UP state and central ministers, and intelligence operatives would be sent to him to pay courtesies, seek his advice on various matters and keep an eye on him," Dhar writes.
The book claims that negative DNA tests concerning the teeth belonging to Bhagwanji were result of fudging by the authorities.
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It also dismissed BJP leader Subramanian Swamy's claim that Netaji was killed in the erstwhile USSR, maintaining that Soviet Union had actually granted asylum to Netaji.
He has quoted Bhagwanji saying that his emergence was "not in India's interest".
'What Happened to Netaji' was released at India Club in central London in the presence of the former Mayor of Harrow, Mrinal Choudhury and president of the Netaji Subhas Foundation UK Suhas Khale.
Meeting long-pending demands, Prime Minister Narendra Modi announced last month that the government will start unveiling the secret files related to Bose from January 23 next year, raising hopes about solving the seven-decade-old mystery about his disappearance.