Illustration: Matt Davidson

Illustration: Matt Davidson

Relations between the Greens and Labor have broken down at both the federal and state level. Last year the Greens withdrew their support from the 2010 agreement with the Gillard Labor government after a considerable period of tense relations. Earlier this month Tasmanian Premier Lara Giddings dismissed the two serving Greens ministers from her government and and replaced them with Labor appointees in preparation for going it alone at an election in March.

This places in jeopardy future alliances between the two parties and must be disturbing for members of the Labor-Greens ACT government. Both actions took place under severe pressure as the respective governments were approaching defeat, but they still raise more general questions about future alignments. Labor and the Greens should be thinking about their future.

These are important political questions because they impact on the shape of the Australian party system, which at the moment has four major parties. Put to one side the independents and emerging players such as the Palmer United Party. The four major parties exist, in the eyes of voters, on a left-right continuum that reads Greens-Labor-Liberal-National.

Roughly speaking the electorate is divided into two halves: Labor-Greens and Liberal-Nationals. In the Labor-Greens half Labor is dominant, and in the Liberal-National half the Liberals hold sway. But neither of the two giants gains a majority of first preference votes. In our preferential voting system this means they depend on the support of their smaller allies. Each of the giant parties would prefer not to rely on their smaller ally but the smaller parties are probably not going to go away.

The two halves of the Australian party system are not symmetrical.

Labor and the Greens suffer because they lack the security of the more settled Liberal-National relationship. The unsettled Labor-Greens relationship is in a particularly bad way at the moment. On the other hand, the Liberal-National coalition is strong at the federal level and in several states.

There are good reasons for this. Labor and the Greens are still very much adversaries, especially in inner-city federal and state electorates where the Greens have been successful and hope to win even more seats in the future. The two parties compete more generally in proportional representation voting systems, including the Senate and the Tasmanian and ACT lower houses. There is no agreed demarcation zone between the two parties as has emerged between the Liberals and the Nationals.

Such a demarcation will not be easy to reach. Look at the Liberals and Nationals for confirmation of this. That relationship has developed over the almost 70 years since the Liberals were created and, in more general terms, over about 100 years since the emergence of the Nationals' predecessor, the Country Party. Labor and the Greens have had about 25 years to come to grips with their potential dancing partner. They have a lot of work to do.

The Liberal-Nationals have now reached the stage where they have amalgamated in Queensland to form the Liberal National Party and are mostly in coalition elsewhere. They also run joint Senate tickets and generally avoid contests against sitting party MPs. But they have reached this stage only after enormous turbulence, including outbreaks such as the Joh for Canberra push in 1987.

The Liberal-National coalition is one model for the centre-left half of Australian politics to think about. In the present climate such a firm alliance seems almost unthinkable but it is a definite possibility even if, as with the centre-right, it takes a long time to achieve and involves sacrifices for both parties.

Why does the Liberal-National coalition work? It has several properties that enable it to work most of the time. The first is that the very real battle to the death between the two long-time adversaries has been put aside. The Nationals have survived the threats to their very existence but they have also come to accept they are a minor, not a major, party. That has been painful for them.

Ideological differences between the two parties still exist on matters including trade and industry and social morality questions but they have been somewhat contained. Demographic changes have also softened but not eliminated the historic social differences between the two parties. The Nationals have been partially absorbed and are not the party they once were.

The Nationals are not considered a big enough electoral liability by the Liberals to justify the dissolution of their coalition. They cause grinding of teeth by more liberal Liberals, but are kept within the family nonetheless.

The Labor-Greens relationship is more volatile and does not yet share these properties. Only continued success will convince the doubters the Greens are here to stay. Until then the battle to the death will continue with Labor hoping the Greens will fade away.

The Greens themselves have not given up the hope of growing from a minor into a major party. Furthermore, as a young party they remain committed to their distinctive policies and orientation.

Finally, many in Labor believe that a close relationship with the Greens should be anathema because the Greens are electorally unpopular enough to damage perceptions of Labor.

This will only change if policies that are currently identified with the Greens - same-sex, for example - become part of the comfortably accepted mainstream Australia-wide.

Time may well make the Labor-Greens relationship a more comfortable one. The federal and Tasmanian breakdowns are quite similar to Liberal-National rumblings in the past. But until then the centre-right of Australian politics is more settled than the centre-left.

John Warhurst is an emeritus professor of political science at the Australian National University.