The greatest support to keep MMP came from Maori voters, while the strongest current for change flowed from staunch National seats, a breakdown of voting by electorates shows.

Official election results confirmed MMP would be retained and reviewed, almost 58 per cent voting in favour.

A breakdown of the electorates showed the seats where MMP was most popular by percentage support were the seven Maori electorates, even though a low turnout meant the actual number of voters was much lower than other electorates.

Support for MMP was strongest in Waiariki at 85.5 per cent, followed by Ikaroa-Rawhiti, Tamaki Makaurau, Te Tai Hauauru, Te Tai Tokerau, Hauraki-Waikato and Te Tai Tonga.


In contrast, the electorates where MMP support was weakest were National strongholds: Clutha-Southland (44.6 per cent), Rodney, Hunua, Helensville, Taranaki-King Country, and Tamaki.

Keep MMP spokeswoman Sandra Grey said the results were not surprising. "Maori have recognised MMP does bring in a much more diverse Parliament, they like that diversity, and then across all parties there is engagement with Maori and Maori communities."

She said weaker support for MMP in bluer seats partly reflected Prime Minister John Key's vote for change.

The challenge for the group was to make sure the public engaged with the review process.

Aspects of the review will include:

The threshold for list seats - currently either a party winning at least 5 per cent of the party vote, or a party candidate winning an electorate seat.

The overhang, where the total number of MPs increases when a party wins a disproportionate number of electorate seats compared to its share of the party vote.

Dual candidacy, where an MP stands in an electorate as well as on the party list, or where a list MP can contest a byelection.

The way a party's list is ranked, and whether voters should have a say.

The effect of population change on proportionality

Not up for review are the number of MPs and Maori representation.

This election, three MPs - National's Chris Auchinvole and Paula Bennett, and Labour's Clayton Cosgrove - lost their electorate seats but return to Parliament on the list.

Prime Minister John Key said he didn't want to pre-judge the review but it was his personal view list MPs who left a party should leave Parliament.

"For example, if you're one of [the Green's] 14 list MPs and you decide, for whatever reason, at some point in the term you're going to become an independent, my view is that you should have to vacate Parliament."

In 2007, list MP Gordon Copeland left United Future and became an independent MP over his opposition to Sue Bradford's child discipline bill.

He was criticised as having no mandate for being an MP, having entered Parliament on United Future's list.