You need to count the green bracts surrounding the flower heads to be certain it is not a native Senecio. Or a sideways on closeup of a flower head so others can do so.
It is essential that you count the bracts. The only obvious diferrence between it and some forms of Senecio pinnatifolius (var. alpinus in the ACT) is the number of bracts around the flower head. http://keyserver.lucidcentral.org/weeds/data/media/Html/senecio_madagascariensis.htm
Mike if following Betty's advice it is still Madagascarian Fireweed can you please pull out and bag plants - given the location I suggest that if in doubt you remove and bag as a matter of urgency