Game, set and match to David Shearer.

Labour's leader still faces a further test in February under his party's new rules in the form of an obligatory caucus motion requiring he obtain the backing of more than 60 per cent of his MPs to avoid triggering a leadership election.

Shearer's securing of unanimous backing in yesterday's ballot on a similar motion at an emergency caucus meeting called by him has effectively made February's vote a formality.

The successful tactic has left David Cunliffe and his supporters now having to decide whether they are willing to sustain the hellfire and damnation that will surely rain down on them if they seriously entertain thoughts of a renewed challenge to Shearer's leadership in the New Year.

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Unfortunately for Cunliffe, there is nothing of note on the horizon between now and February to offer him any leverage to improve his chances of persuading more colleagues to support him.

Mounting a challenge will simply look self-serving if, having backed Shearer yesterday, Cunliffe's supporters then turn around and try to oust the current leader.

For his part, Shearer is playing divide-and-rule. He has disciplined Cunliffe, dumping the New Lynn MP from Labour's front bench and stripping him of his prized economic development and associate finance roles.

Shearer has not given Cunliffe's backers in the caucus the same treatment. He is planning a major reshuffle of Labour's shadow Cabinet. He is clearly leaving those MPs to work out where their best interests lie.

As for Cunliffe, he is now on notice to toe the line. If he continues to exhibit the disloyalty he so openly displayed at Labour's annual conference last weekend, he will be suspended or expelled from the caucus.

He has since found himself on the receiving end of roastings from senior colleagues both in public and in private. Those MPs are simply flagging that they could not work under him. That is the main reason why Cunliffe will not be able to trigger a leadership election in February.

Labour cannot afford to end up with what would be a hopelessly divided caucus. That is not a recipe for good government - or even good Opposition. It would poison Labour's chances of winning the 2014 election.

That is the bottom line. And those few MPs still inclined to back Cunliffe know it.