The dismissal of the Whitlam Government in 1975 has been described as the greatest political crisis in Australia’s history. It began when the Senate refused to pass the government’s budget. The supply crisis and dismissal were possible because a number of longstanding conventions were broken.
Although a constitution is a formal legal document, its operation relies on the use of “conventions” which are accepted practices and unwritten rules. For example, the Prime Minister is not mentioned in the Constitution and neither is the Cabinet but their roles are defined by conventions. Conventions are not laws but are recognised as useful and practical.
In 1975, the perception was that:
Two State governments ignored the convention that when a Senator resigns or dies, State Parliament selects a replacement from the same political party.
The Senate's decision to block supply was considered by many as a breach of the Westminster convention of responsible government.
A longstanding Westminster convention - that the government is formed by the party that that has the confidence of the Lower House and that the Upper House will therefore allow that government the funds to govern - was broken.
The convention, that when the House of Representatives does not support a Prime Minister, the Prime Minister resigns, was not observed.
In dismissing the Whitlam government, Kerr acted within the letter of the Constitution but he did not observe the convention that a Governor-General should act on the advice of the Prime Minister.
The breakdown of conventions, the way people thought the Constitution functioned, contributed to the 1975 constitutional crisis. One change that did result from the crisis was that in 1977, Prime Minister Malcolm Fraser moved a successful referendum to formalise the method of choosing Senate casual vacancies to reflect what it had been assumed the convention had intended.