Nonetheless, Labor - which relies on Greens preferences to win elections - is nervous and angry. Opposition Leader Bill Shorten in Cairns this week. Credit:Alex Ellinghausen "If you are a Green voter in the suburbs and regions of Australia, when you vote Green your vote will be going to the Liberal Party," Opposition Leader Bill Shorten said on Tuesday. He has been repeating the theme. Later on ABC Townsville radio, he said: "A vote for Greens in marginal seats in Victoria, for example, will be funnelled to the Liberal Party." But this claim is rubbish. In fact, it cannot be true, as only you - the voter - can decide where your preferences go. It cannot be "funnelled" anywhere.

In the lower house, mandatory preferential voting means you must label every box in order of preference. That's why those sprightly campaigners thrust how-to-vote flyers into your hands outside polling booths - but you are free to ignore them (and increasingly, people do). The Greens received $3.9 million in donations in 2015-16. Credit:Natalie Grono For their part, the Greens and the Liberals won't say much about the supposed arrangement. Greens figures insist they are not preferencing the Liberals - which is not the allegation - but that open tickets are a matter for local branches. The Libs say nothing is locked in. Still, many people will inevitably take direction from how-to-vote cards, and that's fine too. But does it matter what Greens how-to-vote cards say?

There's a good chance all of this haranguing is over very little, according to the ABC's veteran election analyst Antony Green. In the 2010 federal election, the Greens recommended preferences to Labor in 98 seats and ran open tickets in 44 seats. About 3 per cent more preferences flowed to Labor in the seats where the how-to-votes recommended it, Green found. That is 3 per cent of preferences, not 3 per cent of the total vote. "If the Green first preference vote was 10 per cent, this difference in preference flows would correspond to 0.3 per cent of the overall vote," Green wrote on his blog. "That indicates that in extremely close contests, there is a chance Green preferences could have an impact."

Who really has the final say? But voters ultimately make the final choice. For example, in the western Sydney seat of Lindsay, where the Greens recommended preferences to Labor in 2007, 73 per cent of the Greens' primary votes ended up with Labor's David Bradbury. In 2010, the Greens moved to an open ticket in Lindsay. They received a higher primary vote (Labor was on the nose), but 75 per cent of those votes ended up with Mr Bradbury anyway. In 2013, they switched back to preferencing Labor and preferences flowed at an even higher 82 per cent.

The bottom line? Greens voters generally give their preferences to Labor whether or not they are told to on a how-to-vote card. Can preferences really affect the result? The more important side of this supposed preference "arrangement" between the Greens and the Liberal Party is that the Liberals would recommend preferences to the Greens in urban seats the Greens could actually steal from Labor, such as Anthony Albanese's Grayndler in Sydney and David Feeney's Batman in Melbourne. If the Liberal candidate comes third in those races, those preferences could help a Green topple the incumbent Labor member. Liberals have long debated internally whether this is a good idea. Tactically, it makes it harder for Labor to form government, but ideologically, it elects people further to the Left.