"Withers reveals that not only had Kerr decided to act against Whitlam in the week before 11 November 1975, but that both he and Fraser knew this," Professor Hocking said.

Whitlam died a year ago last Wednesday, Fraser last March, and Professor Hocking's book, The Dismissal Dossier: Everything You Were Never Meant To Know About November 1975 comes out on the eve of the 40th anniversary of what many people still believe to be the biggest political crisis in Australian history.

Professor Hocking said the secret communication was the most serious possible breach of the central constitutional and political relationship in a parliamentary democracy that the Governor-General acts on the advice of the Prime Minister, not the Opposition Leader.

"Fraser told the caller that he could be contacted on that number at any time ... Fraser then asked the caller for their number, repeating as he wrote it down, 'I can also ring you on his number?.... As Fraser hung up he said to Withers. 'You never heard this conversation'."

"It now appears that the very basis of Whitlam's dismissal, and Fraser's appointment, as Prime Minister – the need to secure Supply – was a constitutional and political charade," Professor Hocking said.

"In this previously unpublished interview Fraser makes the extraordinary claim that the provision of Supply was not in fact a condition of his appointment as Prime Minister at all." Fraser makes this devastating admission in his interview conducted in 1987 with former Labor Minister Clyde Cameron for the National Library of Australia that has only recently been made available. "Asked specifically whether the provision of Supply was a condition of his appointment as Prime Minister, Fraser replied without any hesitation, 'No, it wasn't'.

"In a further dramatic historical unravelling Fraser then revealed that, even had he not secured Supply through the Senate on the afternoon of 11 November 1975, Kerr would not have dismissed him as Prime Minister and that he would have gone to the 1975 election as Prime Minister, without Supply. A shocked Clyde Cameron drew out the implications of this startling exchange in his immediate response to Fraser: 'You would have gone to an election without Supply, and you would have been in breach of one of the conditions that Kerr had laid down.' Fraser did not disagree with this, suggesting that the Coalition might even have won a few more seats had he done so.

"Despite Kerr's insistence that securing Supply was at the heart of the dismissal, Fraser maintained that his own failure to secure Supply would not have led to his dismissal and that Kerr would not have dismissed him for a denial of Supply as he had dismissed Whitlam: 'I don't think the Governor-General would have had much other course … I think it would have been a little difficult sacking a second (laughing) Prime Minister and re-appointing the first one sacked'."

Professor Hocking said that Kerr's private papers clearly show that the Palace knew that Kerr was considering the dismissal months before it happened. The Palace did not counsel Kerr against the dismissal scenario, did not advise him to warn Whitlam of the possibility of dismissal and, most significantly, did not themselves alert Whitlam to the fact that the matter had been raised by the Governor-General.