The deals now being hammered out between National and Act make a mockery of Don Brash's pledge on becoming Act leader that he would be aiming for 15 per cent of the party vote.

The two parties have been talking about making accommodations both in the Epsom electorate and in marginal National seats so that National gets a coalition partner and Act avoids political oblivion. With National tracking above 50 per cent in the polls, it's not hard to see who has more to gain.

Brash is plainly having trouble getting any more public support than his benighted predecessor - Act's share of the vote has certainly increased but it is struggling to make 2 per cent, well below the threshold that would carry it back into Parliament on its own merits.

Hence the tactical discussions. Nobody's saying anything out loud, but National will tip their voters a wink to keep out of John Banks' way in Epsom and in return, Act won't field candidates in electorates where it's a close two-horse race between National and Labour.

That's politics of course, and it won't be the first time Act has prospered from the provision in MMP that allows a party's share of the vote under 5 per cent to be counted if it can carry an electorate. In 2008, it had only 3.65 per cent of the popular vote - a figure presumably looming large in Brash's mind; in 2005 it was barely 1.5 per cent.

But it is a matter that will figure in voters' thinking in the run-up to the referendum being held with this year's general election. In the first part of a two-stage poll on the electoral system, voters will be asked if they want to dump MMP in favour of another system (and, whatever their answer to that, what alternative system they would choose, if asked). If there is a mood for change, a 2014 vote will pit MMP against the most popular of the alternatives.

MMP starts the race with something of an advantage: it is the incumbent system and voters prefer the devil they know, and even if it doesn't win a majority of the vote in November, it still gets another chance in 2014.

But it is also hampered because it goes to the public vote with all its shortcomings on show. Justice Minister Simon Power has signalled that even if MMP gets the tick in November, it will be up for a review, but it would be helpful to know what elements might be reviewed, and how, before we are asked to vote whether to keep it.

In various surveys on the question, many voters have said that they are deeply suspicious of the way MPs who have been rejected by an electorate get into Parliament by virtue of a high party-list placing. Others want to see the threshold - albeit a lowered one - be a real threshold: thus a single electorate win for a party with little support would entitle it to just one member's seat.

If recent public opinion polls are any guide, MMP seems unlikely to be seriously challenged, perhaps because there is a promise of an overhaul. Since late 2009, support for retention has grown from barely 37 per cent to more than 50.

In the meantime, voters are far from powerless to punish parties they think are gaming the system, either by giving each other a nod and a wink or by dragging their deadwood in by the back door. The party vote is the one that determines how many list members make the cut. And in voters' hands it remains a menacing weapon.