Metiria Turei has probably long forgotten it. Those who witnessed it still wince at the memory.

Late in April, the Green Party's co-leader was tasked with asking the first Opposition question of the parliamentary day.

A series of gladiatorial duels pitting Labour and Green MPs against Cabinet ministers which sees no quarter given and none asked, question-time is the ultimate and, at times, the cruellest test of a politician's ability to cut it.

National thought Turei was going to target the tenure review of high-country leases and that she had something damaging to drop which would embarrass the Government.

So there was a palpable sense of relief along the National benches when her follow-up question turned out to be a weak jibe at the Government's mining policy.

Turei clearly had nothing up her sleeve to jolt National. She instead tried to develop a bizarre argument that National's stock-take of possible mining sites on the conservation estate amounted to a privatisation of the country's mineral deposits.

Given that private enterprise has always been the dominant force in such mining operations - including those on Conservation Department-administered land - it was difficult to work out what she was getting at. But on she went, feeble supplementary question following feeble supplementary question, seemingly oblivious to the increasingly excruciating nature of her performance in front of the House.

The episode said a lot about Turei's struggle to make an impact since she saw off Sue Bradford to become the party's female co-leader following the retirement of Jeanette Fitzsimons.

It also said a lot about the Greens' struggle for profile generally. Yet the party, which is holding its annual conference this weekend, is arguably having its best run in the polls since entering Parliament in its own right in 1999. On present trends in the polls, the Greens should easily beat the 5 per cent threshold at next year's election and could even get well into double figures in percentage terms of the party vote.

So Turei and company must be doing something right. Indeed, the party is doing some things right. The party's other co-leader, Russel Norman, has almost single-handedly pushed the state of the country's water quality and resources to the forefront of the political agenda.

In the absence of Winston Peters and New Zealand First, he has astutely positioned the Greens as the anti-establishment party talking the language of economic nationalism, most recently in trying to stop the Crafar family farms from falling into Chinese hands.

Norman has also given Turei plenty of room to flourish in the 12 months since she was elected to her post at last year's conference.

That she seems to think she has when the opposite is the case should be of some worry. Of equal concern must be the party's lack of urgency in taking advantage of highly propitious circumstances to build a power base of real strength on the centre-left while Labour is having huge difficulty reconnecting with voters.

The Greens are instead merely cruising in this tail-wind fuelled by a number of high-profile environmental and conservation issues - National's plan for mining on the conservation estate, the wrangling over National's watered-down greenhouse gas emissions trading scheme, and whether New Zealand should compromise its long-held opposition to Japanese whaling in the Southern Ocean.

There is a view shared across other parties that the Greens have failed to nail these issues as their own. That was definitely the case with whaling, which saw Labour's foreign affairs spokesman Chris Carter grab the opportunity to whack National. The Greens were initially unusually silent.

Turei finally produced a statement condemning National's decision to use diplomacy to try to hammer out a compromise between the warring members of the International Whaling Commission. In the Greens' defence, however, the compromise option, for all its faults, had to be treated seriously although it is difficult to pin down the degree of internal debate in the party about that.

Since Fitzsimons quit Parliament, the Greens have been almost invisible in the continuing argument about climate change, leaving a huge gap which Act has filled by taking the reverse stance to the Greens.

The latter have been more active in the mining debate - but this quickly became a very crowded market in which to make yourself heard. Despite that, Labour insiders think the Greens have secured the political rewards from the debate because the Green "brand" is so strong that voters identify with it regardless of which party was putting pressure on the Government to back down.

The trouble is by the time the election rolls around, National will have long backed away from its current intention to allow mining on pristine parts of the conservation estate. This may not be the only issue helping the Greens now which could have disappeared off the agenda by election time.

But at the moment the Greens, rather than Labour, are the ones unquestionably benefiting from any disillusion with National.

This has been helped by the departures of Nandor Tanczos and Bradford and a more moderate leadership making the Greens no longer so scary to voters. Likewise the notion of the Greens being "whacky" rarely gets a play these days.

To the contrary, the party under Fitzsimons' leadership built up vast stocks of credibility for taking principled stands and not indulging in cheap politics. The party's willingness to work with National in areas of common interest has also been a significant factor in making them more acceptable to the mainstream of politics, rather than being ghettoised on Labour's left.

Likewise John Key's willingness to work with the Greens has inevitably changed the way the Greens are viewed by National's supporters.

While the level of co-operation under the two parties' memorandum of understanding has tailed off since last year's joint development of the landmark home insulation scheme, they are still said to be talking about potential joint initiatives in other areas of mutual interest.

The Greens' new respectability has made them a suitable half-way house for middle-ground voters who cannot abide returning to Labour - at least not yet.

Yet, as the election draws ever nearer, the Greens will find it more and more difficult to play on both sides of the fence. They are going to have to declare to their growing number of adherents which of the two major parties they are willing to work with after the election and to what degree.

However, National's tax cuts for the wealthy, its running down of the core public service and its failure to address what the Greens call the "social deficit" have obliterated any slight chance of the Greens propping up a National-led Government on a confidence and supply basis.

Moreover, with Norman and Turei reasserting the Greens' "social justice" agenda, that leaves the party either standing to one side as now or striking a coalition deal or some other support arrangement with Labour.

Inevitably, Labour will reassert itself as a political force as major points of difference emerge between itself and National.

The danger for the Greens is that unless they lock in the gains they are making now, they risk being returned to square one as a bit player. Stuck in cruise control, they could be left straggling in Labour's dust.