Correspondence exchanged between the Queen and her representative in Australia in the lead up to the country’s only dismissal of a former prime minister can be made public, a court has ruled.

The Australian High Court overturned an earlier decision relating to the cache of letters which have been sealed in the National Archives.

Governor-General Sir John Kerr dismissed Labour prime minister Gough Whitlam in 1975 and replaced him with opposition leader Malcolm Fraser in one of the most controversial moments in the country’s political history.

The letters, deemed “personal and confidential correspondence”, were deposited into the National Archives of Australia and were intended to remain private until at least December 2027.

The private secretary of the Governor-General and Monarch at that time could also limit their release under an agreement, court papers said.

Professor Jennifer Hocking had made the case that the letters and telegrams should be released as they constitute “Commonwealth records”.

This would mean publication 31 years after creation, meaning they should have become public in 2006.

However, the Federal Court accepted the Archives’ argument they were “private and personal” to Sir John.

An appeals court upheld that decision, but it was overturned by the High Court on Friday who said the archives should reconsider Professor Hocking’s request to access the letters.

In an event which has since been referred to as The Dismissal, Mr Whitlam was removed from office by Sir John after the Labour leader failed to pass a budget and then opted not to resign or call an election.

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 decision comes five years after the UK’s highest court ruled that secret letters sent by the Prince of Wales to government ministers should be published.

Charles’ correspondence with ministers – known as “black spider” memos – were released in May 2015 following a long-running battle by Guardian newspaper journalist Rob Evans to see the documents following a freedom of information request.

The letters were published with some redactions following the Upper Tribunal’s ruling that it “has accepted Mr Evans’s submission that what is described in the decision as ‘the open material’ is to be supplied to other parties without restriction on their ability to publish that material”.

The decision of the tribunal included a proviso that the material could be published subject to any “provisional redactions” to protect personal data of people other than Charles.