The former governor-general's private records say Sir Anthony ''played the most significant part in my thinking'' and reassured him he had made the right call two days before he dismissed the government on November 11. They also assert that Sir Anthony, at the time a High Court judge, was the author of a statement that Kerr incorporated in his public statement justifying his actions.

The record was uncovered by the Whitlam biographer Jenny Hocking, whose book Gough Whitlam: His Time will be published next month. Hocking says Kerr's records suggest ''Mason was not merely the third man: he was, in many ways, the man''.

Kerr's records make it clear that he wanted the extent of Sir Anthony's role to surface after his own death but while Sir Anthony was still alive, to deflect his responsibility for the deception and dismissal of Mr Whitlam.

''In the light of the enormous and vicious criticism of myself, I should have dearly liked to have had the public evidence during my lifetime of what Mason had said and done during October-November 1975 … [but] he would be happier … if history never came to know of his role,'' he wrote.

''I shall keep the whole matter alive in my mind till the end, and if this document is found among my archives it will mean that my final decision is that truth must prevail, and, as he played a most significant part in my thinking at that critical time, and as he will be in the shades of history when this is read, his role should be known.''

The account adds weight to the perception of Kerr as a weak man who wanted and needed to feel his actions had the approval of others. Aside from being portrayed as a constant confidant, the record depicts Sir Anthony ''as providing a necessary bridge between Kerr and chief justice Sir Garfield Barwick'', the book asserts.

It also describes how Kerr took ''the extreme step'' of raising the possible dismissal of the Whitlam government with Prince Charles in September 1975, when they met in Port Moresby for an event to mark the transition to an

independent Papua New Guinea. ''Neither Kerr nor the palace ever revealed that, weeks before any action in the Senate had been taken [to block supply], the governor-general had already conferred with the palace on the possibility of the future dismissal of the prime minister, securing in advance the response of the palace to it,'' Hocking writes.

Sir Anthony's role in the dismissal has been the subject of speculation for decades, after Kerr noted in his memoir that one person other than Barwick ''sustained me in my own thinking as to the imperative within which I had to act''.

While the Herald columnist Gerard Henderson has reported that Kerr told him he directly consulted Sir Anthony before the dismissal, the detail laid out in Kerr's private papers on their ''running conversation'' staggered Hocking, who researched the biography for seven years.

''This was the discovery that I was most excited and, to an extent, shocked by,'' she told the Herald. ''I was just astonished by what I read.''

Sir Anthony has consistently refused to be drawn on his role and, when again pressed by Hocking, refused to be drawn, telling her: ''I owe history nothing.''

However, Sir Anthony has written his account of what took place and has agreed for it to be published exclusively in the Herald on Monday.