While political observers say it is too early to see the full impact of what the Greens' decision to block legislation will mean to its vote, they do suggest that dealing with the boats will be a big test for the party.

''Now we are in the post-Brown phase for the Greens, do they have the same political adroitness to handle this?'' senior politics lecturer at Monash University Paul Strangio said. ''It has become less morally black and white for left-liberal people and I think it is challenging left-liberal people [who backed the Greens' position] to think about this again.

''It is not morally absolute on either side and it probably is becoming more problematic for the Greens. It is not now as simple for the Greens as saying 'we oppose offshore processing at all cost' because now this other question - how do you stop people getting on boats - has become even more compelling.''

At the 2001 election, which was heavily framed by the Tampa crisis, the Greens' vote increased dramatically, with the issue becoming ''totemic'' for the party.