David Shearer's last round. Ding, ding

With three pretenders to see off and an active destabilisation campaign underway, Shearer's hold on the leadership looks precarious. Does he have one big push left in him? And if not, what happens next?

Labour has long defined itself as the party of change and opportunity, and those concepts will be front of mind for many of the party's MPs while on recess.

With his leadership at the crossroads, David Shearer has – remarkably – gone on holiday. And we all know what happens when leaders go on holiday. 'When the cat's away...' and all that. The whispers can start to coalesce into a tactile conversation about the opportunity for change.

When Shearer returns he may have one last shot at convincing New Zealanders – and therefore his caucus – that he is a Prime Minister-in-waiting. Or perhaps by that time enough of his MPs will have crossed the mental rubicon needed to force the leadership issue. Perhaps he knows this and is figuring out his exit plan. Because given the new complexity of Labour's coup rules, it will matter how he reacts when (and it seems to be when, rather than if) the challenge comes.

What's looking increasingly clear is that the only things holding him in place have been a) marginally acceptable polling and b) the lack of consensus around who might replace him. If either of those things change, the shadow-boxing will be over. Shearer will either have to enter the ring against a direct challenger (or more) or negotiate a way out.

Already the polls have stagnated and the momentum started by NZ Power has ebbed. Shearer is rapidly running out of round in which to land some blows.

Political observers can now say pretty confidently that at least three of his colleagues think they could do the job better than him. And that's where Shearer's leadership looks at most risk. While he confidently (and with a little help) out-played David Cunliffe at last year's conference, I'm not convinced he can put out three fires at once. He had the numbers and a sense of hope then. But three fires suggests the numbers are moving away from him and splitting into other camps.

Those fires come in the form of Cunliffe, Andrew Little and his own deputy, Grant Robertson.

I can't seen anyone else in the frame at this stage, although Shane Jones remains an enigmatic repository of immense political talent. Sadly the best women for the job aren't in parliament – Helen Kelly or Laila Harre.

It's obvious that at least one of those camps is actively agitating for change this year. The series of destablising leaks in recent weeks can't be seen as anything other than tactical and co-ordinated. And the biggest concern for Shearer would be if they are coming from more than one camp.

We've seen TV political editors told Shearer has until spring at the latest. We've had the man-ban leak. And we've had 'the letter leak' to Duncan Garner.

While Garner has been hauled over the coals for his tweet that a coup was on, he's been clear that he had the story from at least two sources. A lot can change in several hours in parliament, and knowing Duncan I'm confident his information reflected "a truth" if not "the truth". He was a little more definitive than was wise, but the indications I have is that Labour MPs were rattled that day and leadership was very much the topic du jour. Garner's smoke certainly tells us there's fire – and as I've said, it's probably broken out in three places.

This recess has allowed Labour to douse the flames of controversey temporarily, but the embers are still burning. Shearer is clearly on notice to rapidly start looking like a winner or move aside for someone who does. The sad fact for the Mt Albert MP is that after 18 months in the job he has revealed good humour, pluck and resilience, but not the qualities sufficient to win an election; at least, not the 2014 election.

I'd be fascinated to see a Shearer surge, a last round fight back. But if he only has a few weeks to turn it around, that looks like Mission Impossible.

So what does this mean for Labour? The good part is that this agitation suggests the party hasn't given up on next year's election. Speculation has been that it would suit all the pretenders to let Shearer lose next year before one of them rebuilt on the ashes of that failure. Robertson would have more time to build his profile, Cunliffe would put his failed (non-)bid further behind him, and Little might have time to win a seat.

But if the internal polls, or electorate mood, or party groundswell, or stumbling speech patterns – or whatever it is that has Labour's MPs seriously discussing leadership change – has got them spooked and ready to fight, then good. For the sake of our democracy and the integrity of the values they represent, each party should fight every election tooth and nail.

The risk is that the rebellion(s) being discussed now simply flow from backroom to caucus room and stop there. Shearer replaced Phil Goff via a process that lacked transparency, rigour and, y'know, the public. If Shearer can't turn back the momentum against him, that surely must change.

Labour must follow its British counterparts and, as the Brits did in 2010 following Gordon Brown's resignation, hold a proper primary. While New Zealand Labour won't want to drag it out for four months as UK Labour did, they should allow time for a full and frank debate that could show voters it still has MPs with spirit, the strength of its convictions and, ultimately, a leader who has a clear mandate from a stable and united party.

There should be TV debates, policy arguments and a genuine contest of ideas.

The other thing Labour MPs, party members and affiliates will have to get their head around is that they don't have to like their boss. It seems too much store has been put in Shearer's likeability and that lesson must be learnt. I mean, who likes Kevin Rudd? We know many MPs didn't like Helen Clark. The more important questions are how's effective, who takes the party in the right direction and who can win.

But that all depends on what's happening now, during recess, and what happens when Shearer returns from his holiday and whether or not he has one last crack left in him.