Professor Richard Toye has questioned the accepted view that Churchill's oratory was received enthusiastically by Britons and was a decisive influence on the nation's willingness to fight on against the Nazis.
His book presents a new take on the politics of the 1940s and says Churchill's speeches generated considerably more controversy and criticism than historians previously thought.
The Roar Of The Lion tells the story of how Churchill's speeches were really received by the public at home and around the world.
Mr Toye's book examines government and unofficial survey evidence and the diaries of ordinary people.
He shows how reactions to Churchill's speeches at the time stimulated and excited but also caused disappointment and criticism."Many people thought that he was drunk during his famous 'finest hour' broadcast and there is little evidence that they made a decisive difference to the British people's will to fight on," he said.
Mr Toye, who works in the Department of History at the University of Exeter, said: "There was not a blanket acceptance and positive reaction. A more measured response to his speeches is in evidence."