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It has just become that much more difficult for the critics of MMP to muster a majority in next year's first referendum on the electoral system.

Some significant finetuning of the intricately constructed two-stage referendum process revealed yesterday by Justice Minister Simon Power has shortened the odds on MMP emerging the victor.

Power's promise to institute a review of the unpopular aspects of MMP if it wins the first "change or no change" referendum is an incentive to vote for the status quo rather than wholesale change.

As there does not seem to be any deep groundswell for such wholesale change, the prospect of a "modified" MMP may be enough to sway those who are still ambivalent about the proportional voting system not to dump on it in the referendum which will be held with next year's election.

Power's post-referendum review of MMP will canvass some of the more contentious features of that system.

Paramount among these is the way MPs who are thumped in their constituencies can get back to Parliament by virtue of a cosy position on their party's list.

Also up for debate will be the rule which removes the 5 per cent threshold if a party wins a constituency seat - a rule which enabled Act to retain a foothold in Parliament in 2008 while New Zealand First, which won more votes but no seats, was dispatched to the political wilderness. Power gets top marks for being scrupulously fair in the way he has established the two-stage referendum process, giving MMP two bites at survival.

He will be criticised for failing to put a limit on how much the pro and anti-MMP brigades can spend before the vote.

That favours the antis, who will probably benefit from being bankrolled by big business.

But that is balanced somewhat by Power having responded to public annoyance with MMP shortcomings.

In a stroke, Power has deprived hard-line opponents of MMP of a fair chunk of their ammunition. But it is only small arms ammunition.

The critics can still use the heavy artillery - that MMP stops politicians implementing unpopular policies which are in the national interest, that list MPs make little contribution to Parliament, that there are too many MPs anyway and, above all, that the minor party tail wags the major party dog.

One thing going for the anti-MMP brigade is the Maori Party's erratic relationship with National.

The loose talk and communication glitches within and between those parties, combined with the oddball mixture of grandstanding followed by backdowns, will become increasingly tiresome for many, especially conservative-minded voters.

Unwilling to punish National and unable to remove the Maori Party from Parliament, they may use next year's referendum as a safety valve through which to vent their frustration - ditching MMP in the process.

Given that MMP was forced on politicians by voters intent on curbing the power of ruling parties, there would be some irony in it being sacrificed in an intemperate voter backlash against one of the smaller parties.