Forming a government - how it works

The Beehive and parliment building. Photo / Mark Mitchell

The potential combinations of government formation under MMP are many and varied. The simplest and quickest would be for a single party to win a majority of the party votes.

But that has not happened since the first MMP election in 1996.

The first talks under MMP in 1996 comprised parallel talks conducted by New Zealand First between National and Labour. They took two months. The fastest talks were in 2008 when the election was held on November 8 and John Key's first Cabinet was sworn in 11 days later so he could jet off to the Apec summit in Peru and on to meetings in London.

Before he was sworn in as Prime Minister, he had signed confidence and supply deals with Act, United Future and the Maori Party, and MPs from those parties were appointed as ministers outside of Cabinet.

Back in 1996, New Zealand First eventually chose National to form a majority coalition Government between two parties.

But since 2002, all other governments have been minority governments. That means that the coalition partners at the Cabinet table, Labour and the Alliance, Labour and the Progressive, then just National, have not had enough support by themselves and have had formal agreements with other parties to pledge their support on confidence and supply.

To be sworn in as prime minister, a party leader has to convince the Governor-General (acting on behalf of the Crown) that he or she would have a majority of votes to win confidence and supply votes when Parliament is reconvened.

The Governor-General will make that decision based on clear public statements from party leaders.

Confidence and supply issues include the Budget, votes that keep the machinery of government running, or votes of great symbolism, such as the vote on the Address in Reply debate in response to the Speech from the Throne that opens each Parliament.

Under the confidence and supply arrangements that have evolved under New Zealand's MMP, support party ministers have to agree only with the ruling party on issues to do with their portfolio. All other votes on legislation is negotiated party by party. That has worked when there has been a large party leading the government and Mr Key has said it would again be his preference.

But Labour leader David Cunliffe has said his preference would be a three-way coalition with the Greens and New Zealand First, meaning they would all be operating under collective Cabinet responsibility.