The Greens will need to bolster its primary vote to roughly 3% above Labor to triumph in Saturday’s byelection in Melbourne, the Greens’ key Victorian election analyst says, as its bid for a first lower house state seat hangs in the balance.

Stephen Luntz — who has conducted an in-depth investigation into likely preference flows from the Melbourne Cup-style 16-candidate field — says Labor hopeful Jennifer Kanis will benefit from flows from the Christian Right (7%) and a three-candidate block comprising African community leader Berhan Ahmed, the S-x Party and Liberal-leaning independent David Nolte (10%), for a combined windfall of around 17%.

By contrast, between 12% and 15% would flow to Greens candidate Cathy Oke from a rival libertarian-leftish bloc led by Crikey founder Stephen Mayne, and including the Democrats, the Secular Party, green-tinged independent Adrian Whitehead and public housing advocate Kate Borland.

Luntz says on average 70% of the “minor 14” will end up going to the party the candidate’s how-to-vote cards recommend, but he expects this to vary — higher for Ahmed and lower for the S-x Party.

Luntz notes that two fringe candidates — socialist candidate Patrick O’Connor and independent Gerrit Schorel-Hlavka — have not recommended preferences, and predicts their votes will split fairly evenly. The donkey vote will flow from Ahmed to Kanis, which was why he anticipates a higher than usual proportion of Ahmed’s vote finishing with Labor.

ReachTEL polling published in The Australian this morning showed Oke only 1.6 percentage points clear on 38.1%, with Kanis on 36.5% — that lead may not be enough to corral the remaining 26%. S-x Party candidate Fiona Patten was on 6.1%, followed by Mayne on 4.3%. Family First was on 3.8% — however this seems high given the party’s disappointing performances in the Fremantle and Albert Park byelections. Former Liberal voters were split evenly between the Greens and Labor tributaries.

A Roy Morgan poll last month placed the Greens on 48.5% — 11% percentage points clear of the Labor Party on 37.5%, while internal Liberal polling in late May pointed to a much closer race.

In addition, informal votes are likely to top 6% owing to the massive field and growing public disillusionment with the formal political process.

The poll — especially if the Greens can get over the line — is likely to be viewed as a referendum on Julia Gillard’s ailing prime ministership in her home state, despite the protestations of senior federal Labor figures.