The MMP electoral system has seen a vibrant and exciting explosion of ethnic diversity in Parliament and to move away from it would only lead to a future referendum to bring it back, a select committee has heard.

Victoria University political scientist Jon Johansson said yesterday he did not support the referendum into MMP because it had led New Zealand to a "far more representative democracy, which is something we should celebrate".

The electoral legislation committee is hearing submissions on next year's referendum, which will ask New Zealanders if they want to retain MMP or move to a different system.

If a majority want to change, a second referendum will be held in 2014 where voters choose between MMP and the most popular of four alternatives.

If the alternative wins a majority, it will come into effect for the 2017 general election.

Dr Johansson said MMP was a fairer system than first past the post, and it had brought more ethnic minorities and female politicians into Parliament.

"The dramatic increase in ethnic representation in the House is one of the most vibrant, progressive changes. MMP is an excellent fit, not just for our current demographics, but more importantly, the dramatically changing nature of our demographics.

"The Prime Minister has talked about needing to kick the tyres on MMP. Rather than kick the tyres, we are putting the car back up for sale.

"If we do in fact vote [for an alternative], there inevitably will be a push for a third referendum, because great chunks of our electorate who are not middle-class white people will find themselves represented less than they are now."

Dr Johansson recommended changing the first option in next year's election from "retaining MMP" to "retaining MMP or a modified MMP".

"Polling has shown a super majority of New Zealanders would like to either retain MMP or see it modified. It is frustrating that the Government has not seen fit to accommodate this most obvious choice."

He recommended a $500,000 cap on campaign spending.

"You only have to have one referendum, or one general election, subverted by the unfettered use of money and your democracy is forever changed," he said.

The bill before the committee has no spending cap.

The committee also heard from Green Party secretary Jon Field, who said a spending cap would ensure a level playing field.

Maori Party president Whatarangi Winiata said any review of MMP should exclude a review of the overhang seats, which are used when a party's number of electorate seats is disproportional to the share of general votes it wins.

* A referendum next year will ask voters if they want to retain MMP or move to a different system.
* If a majority want to change, a second referendum will be held in 2014.
* Voters will have to choose between MMP and four alternatives.
* The alternative that wins the majority will come into effect for the 2017 election.