The figure in the latest Newspoll showing the Greens vote soaring from 12% to 16% was so stark that not even The Australian could ignore it.

This is not only a record poll result for the Greens at a national level, it is on a par with the best Newspoll result for any third party, with the only comparable figure being obtained by the Janine Haines led Democrats in the lead up to the 1990 election. But as was shown back in 1990 and more recently with the Liberal Democrats in the recent UK election, not to mention the Greens themselves in the lead up to the recent Tasmanian election, it is very difficult for third parties to maintain such peaks through until polling day.

However, whilst the Greens may well drop from that 16% peak, the Newspoll reinforces some significant underlying trends. Firstly, the disapproval ratings for the leaders of both the Labor Party and the Liberal-National Party are high and trending upwards. Secondly, the Greens have consistently polled at 10% or higher in most Newspolls over the past two years, not dropping below 9% for over a year.

This might not seem high, but for a third party trying to compete in a two party system, it is. Neither the DLP nor One Nation at their peaks managed to break the 10% barrier at an election, and the Democrats only achieved it once - at the 1990 election, when they polled 11.3% nationally. Tellingly for the ALP, 1990 was the election where they were reduced to running TV advertisements asking Democrat and others voting for the environment to give their second preferences to Labor - a tactic that many believe was pivotal in Labor's narrow victory.

The rise in Greens support has been steady and gradual, which means it has a more solid foundation and is less vulnerable to the rapid drops in support that can plague third parties. So what does a third party with growing and solid support do in this situation?

With greater support comes greater scrutiny and more direct attacks. Lindsay Tanner, the Labor MP most at risk of losing a seat to the Greens, has been directing more and more criticism to the Greens of late. During a recent television interview trying to defend Kevin Rudd's latest broken promise regarding taxpayer funded advertising, his dismissal of the Greens' criticisms became quite shrill, a significant contrast to the measured tone he usually adopts.

In a 2008 speech to the Senate farewelling the Democrats from that chamber, the Liberal's Nick Minchin spoke of the 1990 election, and acknowledged that just ten days out from polling day, former Democrat Leader Janine Haines was on track to win the House of Representatives seat of Kingston - then held by the Labor Party. Minchin was managing the Liberal's campaign at that time, and said he had strongly pushed for the Liberals to direct their preferences to Labor in order to keep the Democrats out. Having failed to convince his party to adopt that approach, he then "ran the most negative campaign that had ever been run", which knocked 10% off Haines' vote in a week and cost her victory.

There is no point feeling aggrieved by this, as it is part of the fiercely competitive nature of politics and it's what a growing third party has to be prepared to encounter. The Greens are certainly aware of this. In the recent Tasmanian election, there was a strong expectation that some last minute attacks would be made. They weren't disappointed, with Labor targeting the most conservative areas of the state with brochures and phone calls falsely accusing the Greens of having a secret plan to legalise heroin. Despite being well prepared to respond to an attack, it is likely that this scare campaign had some negative impact on the Greens vote.

The run of solid poll results strengthens the Greens chances of gaining the Senate balance of power in their own right. The Greens will undoubtedly seek to emphasise the importance of the Senate contest and the need to have a stronger Senate which can more effectively hold a government to account, with a cross bench that will constructively negotiate and properly scrutinise government legislation and programs. This will be the Greens finally supplanting the Democrats in their traditional Senate role.

But whilst that traditional Democrats role of accountability and scrutiny is very important and valued by many people, it is ultimately also quite constraining, as the Democrats discovered. The Greens are preparing to take on that role, as is evident from the approach the Green Senators have adopted over the last few years, but they also clearly see themselves as playing a wider role.

The public's increasing disapproval of Kevin Rudd and Tony Abbott is related as much to concerns about their credibility and believability as it is to their specific policies, and any credible third party would seek to build support by contrasting themselves against this. But a support base built predominantly on a protest vote is not sustainable, as it consists of people voting against some external factor, rather than for the party itself. If the external factor changes, the reason for voting for the third party can disappear.

The challenge for the Greens as a third force growing in popularity is to counter the stereotypes of the party as being just a protest vote or being extremist or single issue. This means much more than being prepared for more attacks from the two old parties or vested interests who feel threatened. It means highlighting a wide ranging and solid package of policies consistent with a progressive philosophical base. Having credible consistent policies is a better shield against attacks than adopting a small target strategy, and it also provides voters with something to believe in and support, rather than just a vehicle for them to register a protest against other parties.

Of course with far fewer resources and far less media exposure than the larger parties, it is enormously difficult for a third party to develop and communicate such policies and messages in a way which will gain traction with the many voters who are not very engaged in political debates. But as the now ex-Liberal, Malcolm Fraser said, life wasn't meant to be easy - and that especially applies when you're a third party in a deeply entrenched two party system. Politics isn't easy and genuine change isn't easy. Commitment and passion can go a long way, but discipline and focus are also crucial. It has been a long haul for the Greens to get this far, but in many ways their work is just beginning.

Andrew Bartlett was a Senator for Queensland from 1997-2008. He is standing as the Greens candidate in the House of Representatives seat of Brisbane at the upcoming federal election.