Former BBC Moscow corrspondent Martin Sixsmith had written a book promising to tell the inside story of the murder of Alexander Litvenko.
The outspoken KGB man was murdered in London in November after being poisoned with a radioactive substance.
Sixsmith's book – The Litvinenko File: The True Story of a Death Foretold – is due to be published by Macmillan on 6 April. According to publisher Macmillan: "As an old Russia hand, Martin Sixsmith knows the Russian underworld well and in this dramatic new book he exposes the key Russian players, most of whom he has known over the years, to give us the answer to the perplexing question: Who killed Litvinenko?
"Myriad theories have been put forward since he died, but the story goes back to 2000 when hostilities were declared between the Kremlin and its political opponents. This is a war that has blown hot and cold for over six years; a war that has pitted some of Russia's strongest, richest men against the most powerful president Russia has had since Josef Stalin."