The Greens would need to rely on the support of the Liberal Party to retain the crucial seat of Melbourne at the next federal election, according to secret internal polling seen by Crikey.

Greens MP and balance-of-power crossbencher Adam Bandt managed to wrench the seat from Labor last August, exploiting the now-dumped Victorian Liberal policy of supporting the Greens ahead of their traditional foes.

But a “seat monitor” poll of 400 voters, completed one-year on by ALP researchers UMR, shows that Labor’s candidate — rumoured to again be recently elected state party president Cath Bowtell — would emerge triumphant with 58% of the two-party preferred vote against Bandt’s 42%, assuming the Liberals’ stick to their policy of putting the Greens last on their how-to-vote cards.

If the Liberals unexpectedly decided to pull a 180 and favour the Greens for strategic reasons, Bandt would hold on in a squeaker — 54% to 46% based on the 2010 Liberal preference flow of 80%.

The data chafes with more recent Galaxy polling, flicked by the Greens to The Sunday Age two weeks ago, indicating Bandt would retain Melbourne 54%-46% without explicit Liberal support. That margin would open up to a resounding 65%-35% if the former federal status quo could somehow be maintained.

But the prospect of a backflip remains distant with the official policy reversal announced two weeks before last November’s state election by Liberal director Tony Nutt playing well with the party’s conservative base.

The UMR data show the ALP’s primary vote in Melbourne holding steady on 38% compared to last August’s result, with the Liberals picking up four percentage points to 25% off the back of a Tony Abbott-led bounce. But it’s sobering news for the Greens, who have seen their raw support dip by three percentage points to 33%, compared to 36% on polling day 2010.

“Without the benefit of the 80% of Liberal preferences that went to Adam Bandt in 2010 (a strategic Liberal decision to put the Greens ahead of Labor), this survey suggests Bandt would struggle to hold the seat of Melbourne — despite the relatively strong personal numbers the federal MP enjoys,” an analysis of the numbers reads.

The UMR poll also brings much-needed relief for former Melbourne constituent Julia Gillard, with a majority of voters (57%) viewing the PM favourably compared to the 73% who rate Tony Abbott negatively. Sixty-four per cent of voters surveyed support a carbon tax.

In general, satisfaction with the current Labor government is 43%, with 46% unsatisfied. Among Liberal voters 83% are unsatisfied and 10% satisfied, with those numbers broadly reversed in the case of Labor voters (70% satisfied, 22% unsatisfied). Among Greens voters, satisfaction and dissatisfaction is split 43% a piece. Forty-one per cent of so-called “soft” voters — important for party strategists as candidates for arm-twisting — are dissatisfied with 39% satisfied.

Among the reasons for dissatisfaction, the carbon tax rates first, followed by “illegal immigration” and “incompetence/mismanagement”.

While Labor would seem a shoo-in, the UMR research acknowledges the “hypothetical nature of survey conditions in seats such as Melbourne” due to the variability of preference decisions.

Labor’s primary vote has dipped 11% since the 2007 election won easily by popular former finance minister Lindsay Tanner.

A spokesperson for Bandt turned the results on their head this morning, accusing Labor of cosying up to the coalition.

“This is a Labor polling company and it was conducted a month before the Galaxy poll, so it needs to be viewed in that context.

“At its highest the poll shows the only way Labor could win back what used to be a heartland seat is by collaborating with the Liberals.

“It is no wonder that senior Labor figures have been publicly advocating a preference swap with the Liberals.”

Still, it seems that the growing ranks of Liberal voters in Melbourne are more inclined to support the ALP over the Greens regardless of any official statewide stitch-up. While 80% of Liberals preferenced Bandt ahead of Bowtell last year, the UMR poll indicates 71% would independently stump for Labor without an official directive.

Since last August’s poll, activists from both left-wing camps have run parallel community outreach programs to corral support.

A local Labor source told Crikey this morning that members would be wearing out their shoe leather to sell the message that the transition to an emissions trading scheme and the National Broadband Network were Labor initiatives.

“Voters in Melbourne are still supportive of the Clean Energy Future legislation and they have not bought the line that it is all down to Adam,” the source said.

When the carbon tax legislation passed the House of Representatives three weeks ago, Greens leader Bob Brown sheeted the victory home to Bandt’s crafty use of the balance of power.

Labor is expected to preselect its candidate in Melbourne in the middle of 2012 to run against Bandt. Despite speculation the former Slater & Gordon lawyer may bail to a certain victory in the third left-leaning Senate spot, Crikey understands he is now highly unlikely to shirk the battle for lower-house supremacy — notwithstanding the lack of leverage in a presumably Coalition-dominated chamber.