Changes to the way the Labour Party elects its leader will make it much harder to mount a coup and effectively guarantees a leader's job is safe in between elections barring a major caucus revolt.
Labour announced the changes yesterday, including giving about 45,000 party members and union affiliate members a vote on the leadership which is currently voted on by MPs only.
Under the new voting system the votes of members and caucus will count for 40 per cent of the vote each and the affiliated unions' vote will count for 20 per cent.
However, only caucus will be able to force a leadership vote and then only in restricted circumstances.
There will be a regular confidence vote within three months after an election but other than that, the only other way the leader can be changed is if two-thirds of caucus sign a petition - a much higher threshold than the simple majority required to roll leaders under the current system.
Leader David Shearer will face a confidence vote next February, as required under Labour's current caucus rules. However, Otago University politics lecturer Bryce Edwards said he would then be safe until after 2014 because any challenger would have to get two-thirds of caucus support.
"This is incumbency protection and that's not necessarily a bad thing. It seems designed to produce stability within the party, to ward off the corrosive speculation of leadership coups."
Mr Shearer welcomed the changes yesterday, saying it would give members a real say in the party which they had asked for.
Party president Moira Coatsworth said parties overseas, such as the Irish Labour Party, used a similar model, which gave a leader a stronger mandate to lead in between the standard confidence votes, but still provided for leaders to be changed in extraordinary circumstances or if there were serious concerns about a leader.
The provisions will also act partly as a safeguard by allowing caucus to eject a leader if the membership and unions use their combined force to elect a leader who is highly unpopular within caucus.
Under the new voting split, if more than 83 per cent of the members and affiliates vote for one candidate, that candidate will win even if caucus unanimously votes for another.
The changes are expected to be made to Labour's constitution at its annual conference in November. Other changes included targeting the types of list candidates the party needed and streamlining the way the list was decided. Labour also intends to establish a new "registered supporter" category, a step below full membership, and to allow groups other than unions to become affiliates.