A landmark case is underway in the Federal Court to determine whether correspondence between the Queen and the Governor-General concerning the 1975 dismissal of the Whitlam government should be released.

The case centres on whether the correspondence, known as the "palace letters" is private and should stay under wraps, or part of the records of a Commonwealth institution and released in the public interest.

Gough Whitlam's son, Anthony Whitlam QC, is arguing the case for the documents to be made public by the National Archives.

Academic and Whitlam biographer, Professor Jenny Hocking, has launched the case for access to what she describes as "the final piece of the puzzle" of the dismissal.

The letters are embargoed until at least 2027, with the Queen holding final veto over their release after that date.

Anthony Whitlam, a strikingly tall man like his father, made his arguments in a clear and even tone, without theatrics.

Professor Hocking's side argued the Governor-General is an institution of the Commonwealth, and therefore his correspondence should be released.

Sir John Kerr was the Governor-General at the time of the dismissal. ( National Archives )

But barrister for the National Archives, Thomas Howe QC, argued there was a "sharp distinction between the institution of the Governor-General and the Governor-General himself".

He said the organisation was right to keep the letters under wraps.

Mr Howe said that in 1977 when then Governor-General Sir John Kerr was writing his memoirs he had his former secretary David Smith copy a set of the "palace letters" in the dead of night.

He argued the episode showed the personal and sensitive nature of the letters, which were kept in a safe.

"The copying of them was highly expressive of an acknowledgement that what he was doing was facilitating a complete copy of them for Sir John Kerr on the basis they were by Sir John and did not comprise part of the official record," Mr Howe said.

On the way into court, Professor Hocking said the letters would throw light on a key political event in history and were of "huge importance to the Australian people".

She said as a result of her legal action, the decision about whether the documents are released will be made by an Australian court, rather than the Queen.