The Queen’s representative in Australia dismissed Prime Minister Gough Whitlam in 1975 “without informing the Palace in advance”, newly released correspondence shows.

The removal of Mr Whitlam, who had failed to pass a budget and then opted not to resign or call an election, has been the subject of ongoing speculation in the 45 years since.

And the letters, which were released following legal proceedings, showed then governor-general Sir John Kerr did not give Mr Whitlam a chance to call an election because he feared he would be sacked himself.

In one of the letters, addressed to the Queen’s private secretary Sir Martin Charteris, Sir John Kerr admitted to taking unilateral action to remove Mr Whitlam without first seeking the Queen’s express permission to act.

He wrote: “I should say I decided to take the step I took without informing the palace in advance because, under the Constitution, the responsibility is mine, and I was of the opinion it was better for Her Majesty not to know in advance, though it is of course my duty to tell her immediately.”

The letters have been released by the National Archives of Australia – which tweeted its website was “temporarily unavailable” on Tuesday due to high demand – following a ruling in the Australian High Court which overturned an earlier decision that deemed the correspondence as “personal” and not state records.

In a letter more than a week after the dismissal, and dated November 20 1975, Sir John writes that Mr Whitlam had told him the crisis could end in a “race to the Palace” and the governor-general “simply could not risk the outcome for the sake of the monarchy”.

He said: “If, in the period of say 24 hours, during which he (Mr Whitlam) was considering his position, he advised the Queen in the strongest of terms that I should be immediately dismissed, the position would then have been that either I would, in fact, be trying to dismiss him while he was trying to dismiss me — an impossible position for the Queen.”

In response to the release of the documents, a Buckingham Palace spokeswoman said: “At Her Majesty’s Coronation on 2 June 1953, the Queen swore an oath to govern the Peoples of Australia ‘according to their respective laws and customs’.

“Throughout her reign, Her Majesty has consistently demonstrated this support for Australia, the primacy of the Australian constitution and the independence of the Australian people, which the release of these letters reflects.

“While the Royal Household believes in the longstanding convention that all conversations between Prime Ministers, Governor Generals and the Queen are private, the release of the letters by the National Archives Australia confirms that neither Her Majesty nor the Royal Household had any part to play in Kerr’s decision to dismiss Whitlam.”

The documents showed an almost constant dialogue between the pair, with Sir Martin writing on November 17 1975 to state the Queen had read “your statement with close attention” and assure Sir John that his confidentiality would be protected.

Sir Martin wrote that he considered Sir John’s actions “cannot easily be challenged from a constitutional point of view however much the politicians will, of course, rage”.

He added: “I have no doubt Mr Whitlam will try to make the constitutional issue the heart and soul of his campaign but as an extremely shrewd politician who does not live very far away from this house said to me on the 11th of November ‘It is never possible to fight an election on one issue’.”

Mr Whitlam had phoned him on the day of the dismissal at 4.15am, Sir Martin wrote.

“He spoke calmly and did not ask me to any approach to the Queen, or indeed to do anything other than the suggestion that I should speak to you to find out what was going on.”

Sir Martin said Sir John had shown “admirable consideration” for the Queen by not informing her prior to the dismissal.

He wrote: “If I may say so with the greatest respect, I believe that in NOT informing the Queen what you intended to do before doing it, you acted not only with perfect constitutional propriety but also with admirable consideration for Her Majesty’s position.”

The removal of Labour leader Mr Whitlam and his replacement by opposition leader Malcolm Fraser marks one of the most controversial moments in Australia’s political history.

The newly sacked Mr Whitlam famously said on the steps of Parliament House in Canberra: “Well may we say ‘God save the Queen’ – because nothing will save the governor-general.”

Sir John cut his five-year term as governor-general short and resigned in December 1977 and eventually moved to London.

The records released cover the period of Sir John’s term in office, 1974–77, and include 212 letters with attachments across more than 1,000 pages.