Parakh, launching his book "Crusader or Conspirator? Coalgate and other Truths", said the prime minister, who was later his immediate political boss and held the portfolio, did little to rein in the ministers responsible for coal allocations.
The charges come barely a couple of days after some explosive remarks on similar lines in another book by the prime minister's former media advisor Sanjaya Baru.
In his "The Accidental Prime Minister: The Making and Unmaking of Manmohan Singh" (Penguin), Baru said that even though Manmohan Singh was incorruptible, the actions of his cabinet colleagues were not only questionable but also that little action was taken to prevent them due to the power on such matters allegedly exercised by Congress president Sonia Gandhi.