Something in the borage family? Phacelia campanularia?
I'm no expert however this looks like a Nodding Violet (Streptocarpus Caulescens). Here's a link to a Gardenign Aust factsheet.
Hi. A bit hard to be sure from the picture but it might be a Nodding Violet or sometimes Cape Primrose. It's botanical name is Streptocarpus caulescens - so it's not actually a real violet but the flower is violet like. If it is the Nodding Violet it will self-seed in the right conditions but it will never become very invasive.
It's since been identified by a botanist friend as Barleria obtusa of the Acanthaceae family. Also know as the Bush Violet. Could also be a related species Barleria cristata (Philippine Violet). Both are known as potential invasive weed varieties due to the ease of adaption to Australian bushland and their already frequent occurrence in bushland.