The short history of MMP has illustrated how small support parties in a coalition government need to differentiate themselves to avoid damage at the ballot box. For Act, that should, in theory, not have been too difficult a task.

The National Party's shift towards the centre of the political spectrum has left it vacant territory and a constituency on the right. Act's annual conference demonstrated just how much it had muffed matters.

It now finds itself having to go to the extreme of using National as a political punching bag as, somewhat ironically, it stakes out positions that it hopes will appeal sufficiently to continue to make it relevant to National.

At the conference, current and former Act MPs lambasted National for taking easy options in its fiscal management and for succumbing too readily to the Maori Party over the marine and coastal area legislation.

Act leader Rodney Hide said the party would allow mining in national parks and on high-value conservation land to unlock the "hundreds of billions of dollars" in wealth desperately needed to bolster the economy. National, he claimed, had lost its nerve in failing to pursue this option.

Mr Hide can hardly believe the mining of national parks is a realistic prospect. The public outcry that greeted National's tentative move in that direction offered evidence enough of the extent of the opposition. Nor will there be a huge constituency for the other views enunciated at the weekend.

But Act does not need huge support to remain useful to National. If its wretched record over the past couple of years means it cannot entertain the thought of retaining its present total of five MPs at the general election, even the return of two representatives to Parliament would probably make it a worthwhile proposition for National.

That outcome would depend on Act retaining Mr Hide's Epsom seat and attracting a little more in the party vote than the 1.3 per cent it received in the latest TVNZ poll. Neither is a foregone conclusion. It has been polling as low as 0.5 per cent.

There is also the matter of Mr Hide's battered reputation. His taxpayer-funded overseas travel with the girlfriend who is now his wife, the toppling of deputy leader Heather Roy, the resignation of MP David Garrett after his court appearance for fraudulently obtaining a passport was revealed, and ill-judged ventures into populism have eroded support for Act, not least in Epsom.

At the last election, voters there were content to vote strategically for Mr Hide, giving the National candidate their party vote. There is much less appetite for that now. He has a considerable repair job on his hands.

It seems fair to assume National would win the seat if it stood a good candidate against him and campaigned seriously. The Act leader must convince National that he can deliver at least two MPs as the basis for a further confidence and supply agreement, a figure that could yet prove crucial in the post-election forging of a coalition.

There is always a niche constituency for Act's ideology of individual freedom, personal responsibility, strictly limited government spending, and lower taxes. At the last election, it garnered the party 3.65 per cent of the vote.

It must now aim to retain enough of that constituency by revisiting its core principles and staking out the territory to the right of National. That means attracting those voters who believe John Key is being far too diffident and is failing to initiate real reform. The mining of national parks, however much a non-starter in reality, fits neatly into that scenario.

The Botany byelection confirmed the extent of Act's woes. If it is to survive the general election, it must up the ante. Lashing out as it has done will have little or no effect on National's position of strength. It is, however, Act's only chance of re-establishing itself as a party worthy of salvage.