The ALP is “unlikely” to contest the imminent Sydney byelection triggered by the forced resignation of veteran MP Clover Moore.

As the recently re-elected Lord Mayor prepares to farewell the NSW Parliament early this afternoon, Crikey can reveal that NSW Labor is seriously considering sitting out the byelection race because its presence on the ballot paper would help elevate Liberal Shayne Mallard to the Macquarie Street bearpit.

Moore, an Independent, is expected to anoint Australians for Marriage Equality head Alex Greenwich as her successor. Under the NSW system of optional preferential voting, it’s likely that up to half the votes in the ALP pile would exhaust, effectively splitting the progressive non-Tory vote.

Greenwich, whose media profile has soared in recent weeks as federal Parliament mulls four separate gay marriage bills, would almost certainly end up with a bolstered primary if Labor remained on the sidelines. A senior Labor source told Crikey it would be “madness for the Labor Party to invest time and money to help elect a Liberal to state parliament”.

“The Liberal Party will win if Labor runs … if Labor doesn’t it’s really tight between Alex and the Lib. The path to Liberal victory is quite simple — it’s to split the progressive vote,” the source said.

“Labor would be much better off focusing on an education cuts campaign in outer Western Sydney.”

Labor’s state electoral council will meet at 6:30pm tonight and is expected to debate the decision. However, the state branch, led by General Secretary Sam Dastyari, is yet to even call for nominations for preselection for the poll, which is expected in November or early December.

Potential Sydney Labor candidate Cameron Murphy slammed the decision to vacate the space this morning, saying that local branches, charged with ruling on a preselection, “had clearly expressed that they want to run”.

“There ought to be a rank and file presentation. I just think that a decision like this would never be made if we were talking about Newcastle or Blacktown. Branches have been waiting for months for the process to kick off and nothing’s happened.”

Other potential candidates, revealed by Crikey earlier this month, are the CPSU’s Ashley Ubrihien and refugee barrister Shane Prince.

But there may be other factors at play. Labor Left sources accused head office of spending too much cash on the recent byelection in the safe NSW seat of Heffron — a Labor Right fiefdom assumed by former Botany Mayor and factional powerbroker Ron Hoenig.

This analysis by pseph bloggers Poliquant shows how difficult a Labor party victory would be given the need to both campaign against and secure preferences from the Greens in order to get within 5% of Mallard and then vault him on preferences. It also identifies the “x factor” in Moore’s expected tapping of Greenwich.

ABC election analyst Antony Green told Crikey this morning that the primary vote would likely split 35-40% for the Liberals’ Mallard and about 20% between Greenwich, the Greens’ Chris Harris and a Labor candidate, in which case the “Liberals would win with relative ease”. It was “probably” more likely that a Labor decision not to run would assist Greenwich and damage Mallard.

“If Labor can’t win the seat it would be in their interests to act in such a way that if the Liberals can be defeated that the candidate that defeats them, suits them.”

The byelection will take place because of Barry O’Farrell’s controversial “Get Clover” law that bans MPs from simultaneously sitting as elected local government councillors.